diff --git a/package.json b/package.json
index 3caafd20e6..9b5575fb9a 100644
--- a/package.json
+++ b/package.json
@@ -66,7 +66,7 @@
     }
   },
   "scripts": {
-    "start": "http-server -p 9876 --silent",
+    "start": "http-server -a \"\" -p 9876 --silent",
     "develop": "grunt dev --force",
     "api-docs": "jsdoc --configure .jsdoc.json",
     "build": "grunt",
diff --git a/test/commons/color/get-background-color.js b/test/commons/color/get-background-color.js
index fb76e89328..e20abb6d43 100644
--- a/test/commons/color/get-background-color.js
+++ b/test/commons/color/get-background-color.js
@@ -4,18 +4,34 @@ describe('color.getBackgroundColor', function () {
   var fixture = document.getElementById('fixture');
 
   var shadowSupported = axe.testUtils.shadowSupport.v1;
-  var origBodyBg;
-  var origHtmlBg;
 
-  before(function () {
-    origBodyBg = document.body.style.background;
-    origHtmlBg = document.documentElement.style.background;
+  /**
+   * Assert that two Colors are close-to-equal.
+   * @param {axe.commons.color.Color[]} actual
+   * @param {axe.commons.color.Color[]} expected
+   * @param {number} threshold How much each RGB value may differ by
+   * @param {number} alphaThreshold How much the alpha channel may differ by
+   */
+  function assertColorsClose(
+    actual,
+    expected,
+    threshold = 0.5,
+    alphaThreshold = 0.1
+  ) {
+    assert.closeTo(actual.red, expected.red, threshold, 'red');
+    assert.closeTo(actual.green, expected.green, threshold, 'green');
+    assert.closeTo(actual.blue, expected.blue, threshold, 'blue');
+    assert.closeTo(actual.alpha, expected.alpha, alphaThreshold, 'alpha');
+  }
+
+  beforeEach(function () {
+    // This normalizes the default mocha behavior of setting a different background
+    // based on prefers-color-scheme settings.
+    document.body.style.background = '#fff';
+    document.documentElement.style.background = 'unset';
   });
 
   afterEach(function () {
-    document.body.style.background = origBodyBg;
-    document.documentElement.style.background = origHtmlBg;
-
     axe.commons.color.incompleteData.clear();
     axe._tree = undefined;
   });
@@ -31,10 +47,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(128, 0, 0, 1);
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -55,11 +68,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(64, 64, 0, 1);
-
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
     assert.deepEqual(bgNodes, [target, pos]);
   });
 
@@ -75,10 +84,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(64, 64, 0, 1);
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
     assert.deepEqual(bgNodes, [target, under]);
   });
 
@@ -101,11 +107,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(64, 64, 0, 1);
-
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
     assert.deepEqual(bgNodes, [target, under]);
   });
 
@@ -120,10 +122,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(64, 64, 0, 1);
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
     assert.deepEqual(bgNodes, [target, parent]);
   });
 
@@ -138,10 +137,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(64, 64, 0, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.deepEqual(bgNodes, [target, parent]);
   });
 
@@ -155,10 +151,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(102, 153, 51, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
   });
 
   it('should apply opacity from an ancestor not in the element stack', function () {
@@ -173,10 +166,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(102, 153, 51, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
   });
 
   it('should return null if containing parent has a background image and is non-opaque', function () {
@@ -195,16 +185,13 @@ describe('color.getBackgroundColor', function () {
     assert.equal(axe.commons.color.incompleteData.get('bgColor'), 'bgImage');
   });
 
-  it('should return white if transparency goes all the way up to document', function () {
+  it('should return body color if transparency goes all the way up to document', function () {
     fixture.innerHTML = '<div id="target" style="height: 10px; width: 30px;">';
     var target = fixture.querySelector('#target');
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target);
     var expected = new axe.commons.color.Color(255, 255, 255, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
   });
 
   it('should return null if there is a background image', function () {
@@ -272,10 +259,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(0, 128, 0, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.deepEqual(bgNodes, [target]);
   });
 
@@ -324,9 +308,8 @@ describe('color.getBackgroundColor', function () {
       document.getElementById('target'),
       []
     );
-    assert.equal(Math.round(actual.blue), 255);
-    assert.equal(Math.round(actual.red), 255);
-    assert.equal(Math.round(actual.green), 255);
+    var expected = new axe.commons.color.Color(255, 255, 255);
+    assertColorsClose(actual, expected);
   });
 
   it('should return null if an absolutely positioned element partially obsures background', function () {
@@ -362,10 +345,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(243, 243, 243, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -384,10 +364,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(243, 243, 243, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -406,10 +383,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(243, 243, 243, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -428,10 +402,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(243, 243, 243, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -450,10 +421,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(243, 243, 243, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -472,10 +440,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(243, 243, 243, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -491,10 +456,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(255, 255, 255, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.notEqual(bgNodes, [parent]);
   });
 
@@ -508,10 +470,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(0, 0, 0, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
   });
 
   it('handles nested inline elements in the middle of a text', function () {
@@ -527,10 +486,8 @@ describe('color.getBackgroundColor', function () {
     var bgNodes = [];
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
-    assert.equal(actual.red, 0);
-    assert.equal(actual.green, 255);
-    assert.equal(actual.blue, 255);
-    assert.equal(actual.alpha, 1);
+    var expected = new axe.commons.color.Color(0, 255, 255, 1);
+    assert.deepEqual(actual, expected);
   });
 
   it('should return null for inline elements with position:absolute', function () {
@@ -560,10 +517,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(255, 255, 255, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.notEqual(bgNodes, [parent]);
   });
 
@@ -586,10 +540,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
     var expected = new axe.commons.color.Color(243, 243, 243, 1);
-    assert.equal(actual.red, expected.red);
-    assert.equal(actual.green, expected.green);
-    assert.equal(actual.blue, expected.blue);
-    assert.equal(actual.alpha, expected.alpha);
+    assert.deepEqual(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -609,10 +560,7 @@ describe('color.getBackgroundColor', function () {
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
 
     var expected = new axe.commons.color.Color(255, 255, 255, 1);
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -630,10 +578,7 @@ describe('color.getBackgroundColor', function () {
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
 
     var expected = new axe.commons.color.Color(255, 255, 255, 1);
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -655,10 +600,7 @@ describe('color.getBackgroundColor', function () {
 
     assert.deepEqual(bgNodes, [shifted]);
 
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
   });
 
   it('should return null when encountering background images during visual traversal', function () {
@@ -715,10 +657,7 @@ describe('color.getBackgroundColor', function () {
 
     var expected = new axe.commons.color.Color(0, 0, 0, 1);
 
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
   });
 
   it('returns negative z-index elements when body has a background', function () {
@@ -736,10 +675,7 @@ describe('color.getBackgroundColor', function () {
 
     var expected = new axe.commons.color.Color(0, 0, 0, 1);
 
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
   });
 
   it('should return null for negative z-index element when html and body have a background', function () {
@@ -768,11 +704,7 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(fixture, []);
     var expected = new axe.commons.color.Color(255, 255, 255, 1);
-
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
   });
 
   it('should return the body bgColor when content does not overlap', function () {
@@ -783,11 +715,8 @@ describe('color.getBackgroundColor', function () {
     axe.testUtils.flatTreeSetup(fixture);
     var target = fixture.querySelector('#target');
     var actual = axe.commons.color.getBackgroundColor(target, []);
-
-    assert.closeTo(actual.red, 255, 0);
-    assert.closeTo(actual.green, 255, 0);
-    assert.closeTo(actual.blue, 255, 0);
-    assert.closeTo(actual.alpha, 1, 0);
+    var expected = new axe.commons.color.Color(255, 255, 255, 1);
+    assert.deepEqual(actual, expected);
   });
 
   it('should return the html canvas inherited from body bgColor when element content does not overlap with body', function () {
@@ -801,17 +730,16 @@ describe('color.getBackgroundColor', function () {
     document.body.style.background = '#000';
     document.body.style.margin = 0;
 
-    axe.testUtils.flatTreeSetup(fixture);
-    var target = fixture.querySelector('#target');
-    var actual = axe.commons.color.getBackgroundColor(target, []);
-
-    assert.closeTo(actual.red, 0, 0);
-    assert.closeTo(actual.green, 0, 0);
-    assert.closeTo(actual.blue, 0, 0);
-    assert.closeTo(actual.alpha, 1, 0);
-
-    document.body.style.height = originalHeight;
-    document.body.style.margin = originalMargin;
+    try {
+      axe.testUtils.flatTreeSetup(fixture);
+      var target = fixture.querySelector('#target');
+      var actual = axe.commons.color.getBackgroundColor(target, []);
+      var expected = new axe.commons.color.Color(0, 0, 0, 1);
+      assert.deepEqual(actual, expected);
+    } finally {
+      document.body.style.height = originalHeight;
+      document.body.style.margin = originalMargin;
+    }
   });
 
   it('should return the html canvas bgColor when element content does not overlap with body', function () {
@@ -824,16 +752,15 @@ describe('color.getBackgroundColor', function () {
     document.body.style.background = '#0f0';
     document.documentElement.style.background = '#f00';
 
-    axe.testUtils.flatTreeSetup(fixture);
-    var target = fixture.querySelector('#target');
-    var actual = axe.commons.color.getBackgroundColor(target, []);
-
-    assert.closeTo(actual.red, 255, 0);
-    assert.closeTo(actual.green, 0, 0);
-    assert.closeTo(actual.blue, 0, 0);
-    assert.closeTo(actual.alpha, 1, 0);
-
-    document.body.style.height = originalHeight;
+    try {
+      axe.testUtils.flatTreeSetup(fixture);
+      var target = fixture.querySelector('#target');
+      var actual = axe.commons.color.getBackgroundColor(target, []);
+      var expected = new axe.commons.color.Color(255, 0, 0, 1);
+      assert.deepEqual(actual, expected);
+    } finally {
+      document.body.style.height = originalHeight;
+    }
   });
 
   it('should apply mix-blend-mode', function () {
@@ -870,10 +797,8 @@ describe('color.getBackgroundColor', function () {
       var target = shadow.querySelector('#shadowTarget');
       var actual = axe.commons.color.getBackgroundColor(target, []);
 
-      assert.closeTo(actual.red, 0, 0);
-      assert.closeTo(actual.green, 0, 0);
-      assert.closeTo(actual.blue, 0, 0);
-      assert.closeTo(actual.alpha, 1, 0);
+      var expected = new axe.commons.color.Color(0, 0, 0, 1);
+      assert.deepEqual(actual, expected);
     }
   );
 
@@ -890,11 +815,8 @@ describe('color.getBackgroundColor', function () {
 
       var target = shadow.querySelector('#shadowTarget');
       var actual = axe.commons.color.getBackgroundColor(target, [], false);
-
-      assert.equal(actual.red, 0);
-      assert.equal(actual.green, 0);
-      assert.equal(actual.blue, 0);
-      assert.equal(actual.alpha, 1);
+      var expected = new axe.commons.color.Color(0, 0, 0, 1);
+      assert.deepEqual(actual, expected);
     }
   );
 
@@ -911,11 +833,7 @@ describe('color.getBackgroundColor', function () {
       axe.testUtils.flatTreeSetup(fixture);
       var actual = axe.commons.color.getBackgroundColor(target, []);
       var expected = new axe.commons.color.Color(0, 0, 0, 1);
-
-      assert.equal(actual.red, expected.red);
-      assert.equal(actual.green, expected.green);
-      assert.equal(actual.blue, expected.blue);
-      assert.equal(actual.alpha, expected.alpha);
+      assert.deepEqual(actual, expected);
     }
   );
 
@@ -933,10 +851,8 @@ describe('color.getBackgroundColor', function () {
       var target = shadow.querySelector('#shadowTarget');
       axe.testUtils.flatTreeSetup(fixture);
       var actual = axe.commons.color.getBackgroundColor(target, []);
-      assert.equal(actual.red, 255);
-      assert.equal(actual.green, 255);
-      assert.equal(actual.blue, 255);
-      assert.equal(actual.alpha, 1);
+      var expected = new axe.commons.color.Color(255, 255, 255, 1);
+      assert.deepEqual(actual, expected);
     }
   );
 
@@ -954,10 +870,8 @@ describe('color.getBackgroundColor', function () {
       var elm2 = document.querySelector('#elm2');
       axe.testUtils.flatTreeSetup(fixture);
       var actual = axe.commons.color.getBackgroundColor(elm2, []);
-      assert.equal(actual.red, 0);
-      assert.equal(actual.blue, 0);
-      assert.equal(actual.green, 0);
-      assert.equal(actual.alpha, 1);
+      var expected = new axe.commons.color.Color(0, 0, 0, 1);
+      assert.deepEqual(actual, expected);
     }
   );
 
@@ -983,10 +897,8 @@ describe('color.getBackgroundColor', function () {
       var elm3 = shadow2.querySelector('#elm3');
       axe.testUtils.flatTreeSetup(fixture);
       var actual = axe.commons.color.getBackgroundColor(elm3, []);
-      assert.closeTo(actual.red, 128, 2);
-      assert.closeTo(actual.blue, 128, 2);
-      assert.closeTo(actual.green, 128, 2);
-      assert.closeTo(actual.alpha, 1, 0);
+      var expected = new axe.commons.color.Color(128, 128, 128, 1);
+      assertColorsClose(actual, expected, 2, 0);
     }
   );
 
@@ -1002,10 +914,8 @@ describe('color.getBackgroundColor', function () {
       axe.testUtils.flatTreeSetup(fixture);
       var target = shadow.querySelector('#shadowTarget');
       var actual = axe.commons.color.getBackgroundColor(target, []);
-      assert.equal(actual.red, 0);
-      assert.equal(actual.green, 0);
-      assert.equal(actual.blue, 0);
-      assert.equal(actual.alpha, 1);
+      var expected = new axe.commons.color.Color(0, 0, 0, 1);
+      assert.deepEqual(actual, expected);
     }
   );
 
@@ -1036,10 +946,8 @@ describe('color.getBackgroundColor', function () {
       axe.testUtils.flatTreeSetup(fixture);
       var linkElm = div.querySelector('a');
       var actual = axe.commons.color.getBackgroundColor(linkElm, []);
-      assert.equal(actual.red, 0);
-      assert.equal(actual.green, 0);
-      assert.equal(actual.blue, 0);
-      assert.equal(actual.alpha, 1);
+      var expected = new axe.commons.color.Color(0, 0, 0, 1);
+      assert.deepEqual(actual, expected);
     }
   );
 
@@ -1056,10 +964,7 @@ describe('color.getBackgroundColor', function () {
 
     // is 128 without the shadow
     var expected = new axe.commons.color.Color(145, 0, 0, 1);
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
     assert.deepEqual(bgNodes, [parent]);
   });
 
@@ -1072,11 +977,8 @@ describe('color.getBackgroundColor', function () {
     var bgNodes = [];
     axe.testUtils.flatTreeSetup(fixture);
     var actual = axe.commons.color.getBackgroundColor(target, bgNodes);
-
-    assert.equal(actual.red, 0);
-    assert.equal(actual.green, 0);
-    assert.equal(actual.blue, 0);
-    assert.equal(actual.alpha, 1);
+    var expected = new axe.commons.color.Color(0, 0, 0, 1);
+    assert.deepEqual(actual, expected);
   });
 
   it('ignores text-shadows thinner than shadowOutlineEmMax', function () {
@@ -1091,10 +993,7 @@ describe('color.getBackgroundColor', function () {
 
     // is 128 without the shadow
     var expected = new axe.commons.color.Color(145, 0, 0, 1);
-    assert.closeTo(actual.red, expected.red, 0.5);
-    assert.closeTo(actual.green, expected.green, 0.5);
-    assert.closeTo(actual.blue, expected.blue, 0.5);
-    assert.closeTo(actual.alpha, expected.alpha, 0.1);
+    assertColorsClose(actual, expected);
   });
 
   describe('body and document', function () {
@@ -1108,11 +1007,7 @@ describe('color.getBackgroundColor', function () {
         []
       );
       var expected = new axe.commons.color.Color(255, 0, 0, 1);
-
-      assert.closeTo(actual.red, expected.red, 0.5);
-      assert.closeTo(actual.green, expected.green, 0.5);
-      assert.closeTo(actual.blue, expected.blue, 0.5);
-      assert.closeTo(actual.alpha, expected.alpha, 0.1);
+      assertColorsClose(actual, expected);
     });
 
     it('returns the body background even when the body is MUCH larger than the screen', function () {
@@ -1126,10 +1021,7 @@ describe('color.getBackgroundColor', function () {
       );
       var expected = new axe.commons.color.Color(255, 0, 0, 1);
 
-      assert.closeTo(actual.red, expected.red, 0.5);
-      assert.closeTo(actual.green, expected.green, 0.5);
-      assert.closeTo(actual.blue, expected.blue, 0.5);
-      assert.closeTo(actual.alpha, expected.alpha, 0.1);
+      assertColorsClose(actual, expected);
     });
 
     it('returns the html background', function () {
@@ -1145,10 +1037,7 @@ describe('color.getBackgroundColor', function () {
       document.body.removeAttribute('style');
       var expected = new axe.commons.color.Color(0, 255, 0, 1);
 
-      assert.closeTo(actual.red, expected.red, 0.5);
-      assert.closeTo(actual.green, expected.green, 0.5);
-      assert.closeTo(actual.blue, expected.blue, 0.5);
-      assert.closeTo(actual.alpha, expected.alpha, 0.1);
+      assertColorsClose(actual, expected);
     });
 
     it('returns the html background when body does not cover the element', function () {
@@ -1164,10 +1053,7 @@ describe('color.getBackgroundColor', function () {
       );
       var expected = new axe.commons.color.Color(0, 255, 0, 1);
 
-      assert.closeTo(actual.red, expected.red, 0.5);
-      assert.closeTo(actual.green, expected.green, 0.5);
-      assert.closeTo(actual.blue, expected.blue, 0.5);
-      assert.closeTo(actual.alpha, expected.alpha, 0.1);
+      assertColorsClose(actual, expected);
     });
 
     it('returns the body background when body does cover the element', function () {
@@ -1182,10 +1068,7 @@ describe('color.getBackgroundColor', function () {
       );
       var expected = new axe.commons.color.Color(0, 0, 255, 1);
 
-      assert.closeTo(actual.red, expected.red, 0.5);
-      assert.closeTo(actual.green, expected.green, 0.5);
-      assert.closeTo(actual.blue, expected.blue, 0.5);
-      assert.closeTo(actual.alpha, expected.alpha, 0.1);
+      assertColorsClose(actual, expected);
     });
 
     it('returns both the html and body background if the body has alpha', function () {
@@ -1200,10 +1083,7 @@ describe('color.getBackgroundColor', function () {
       );
       var expected = new axe.commons.color.Color(0, 128, 128, 1);
 
-      assert.closeTo(actual.red, expected.red, 0.5);
-      assert.closeTo(actual.green, expected.green, 0.5);
-      assert.closeTo(actual.blue, expected.blue, 0.5);
-      assert.closeTo(actual.alpha, expected.alpha, 0.1);
+      assertColorsClose(actual, expected);
     });
   });
 });
diff --git a/test/commons/color/get-foreground-color.js b/test/commons/color/get-foreground-color.js
index 50b7ea5526..06b31cc752 100644
--- a/test/commons/color/get-foreground-color.js
+++ b/test/commons/color/get-foreground-color.js
@@ -10,6 +10,12 @@ describe('color.getForegroundColor', () => {
     assert.closeTo(actual.alpha, expected.alpha, margin / 255);
   }
 
+  beforeEach(() => {
+    // This normalizes the default mocha behavior of setting a different background
+    // based on prefers-color-scheme settings.
+    document.body.style.background = '#fff';
+  });
+
   afterEach(() => {
     axe.commons.color.incompleteData.clear();
     document.body.scrollTop = 0;
diff --git a/test/commons/dom/get-visible-child-text-rects.js b/test/commons/dom/get-visible-child-text-rects.js
index 242e9453be..126e79d037 100644
--- a/test/commons/dom/get-visible-child-text-rects.js
+++ b/test/commons/dom/get-visible-child-text-rects.js
@@ -14,20 +14,20 @@ describe('dom.getVisibleChildTextRects', () => {
   }
 
   /**
-   * Asset that two DOMRect arrays are equal.
-   * @param {DOMRect[]} rectAs
-   * @param {DOMRect[]} rectBs
+   * Assert that two DOMRect arrays are equal.
+   * @param {DOMRect[]} actualRects
+   * @param {DOMRect[]} expectedRects
    */
-  function assertRectsEqual(rectAs, rectBs) {
-    assert.equal(rectAs.length, rectBs.length);
-    rectAs.forEach((rect, index) => {
-      const rectA = rectAs[index];
-      const rectB = rectBs[index];
-
-      assert.approximately(rectA.left, rectB.left, 1);
-      assert.approximately(rectA.top, rectB.top, 1);
-      assert.approximately(rectA.width, rectB.width, 1);
-      assert.approximately(rectA.height, rectB.height, 1);
+  function assertRectsEqual(actualRects, expectedRects) {
+    assert.equal(actualRects.length, expectedRects.length);
+    actualRects.forEach((rect, index) => {
+      const actual = actualRects[index];
+      const expected = expectedRects[index];
+
+      assert.approximately(actual.left, expected.left, 1, 'left');
+      assert.approximately(actual.top, expected.top, 1, 'top');
+      assert.approximately(actual.width, expected.width, 1, 'width');
+      assert.approximately(actual.height, expected.height, 1, 'height');
     });
   }
 
diff --git a/test/integration/full/dialog/dialog.html b/test/integration/full/dialog/dialog.html
index e1168db4cf..07847f14d3 100644
--- a/test/integration/full/dialog/dialog.html
+++ b/test/integration/full/dialog/dialog.html
@@ -22,12 +22,12 @@
   <body>
     <div id="target">
       <button id="root-button"></button>
-      <div style="background-color: #333">
+      <div style="background-color: #333; color: #000">
         <span id="root-color">Contrast failure</span>
       </div>
       <dialog>
         <button id="dialog-button"></button>
-        <div style="background-color: #333">
+        <div style="background-color: #333; color: #000">
           <span id="dialog-color">Contrast failure</span>
         </div>
       </dialog>
diff --git a/test/testutils.js b/test/testutils.js
index 843441bbf4..d0b7af2b8b 100644
--- a/test/testutils.js
+++ b/test/testutils.js
@@ -17,6 +17,11 @@ var originalAudit = axe._audit;
 var originalRules = axe._audit.rules;
 var originalCommons = (commons = axe.commons);
 
+// Global chai configuration
+if (window.chai) {
+  window.chai.config.truncateThreshold = 0;
+}
+
 // add fixture to the body if it's not already
 var fixture = document.getElementById('fixture');
 if (!fixture) {
@@ -597,8 +602,9 @@ if (typeof beforeEach !== 'undefined' && typeof afterEach !== 'undefined') {
       }
     }
 
-    // reset body styles
+    // reset html and body styles
     document.body.removeAttribute('style');
+    document.documentElement.removeAttribute('style');
   });
 }