BUG: Fix scatter plot colors in groupby context to match line plot behavior (pandas-dev#59846)

Author: myenugula

doc/source/whatsnew/v3.0.0.rst

@@ -798,6 +798,7 @@ Plotting
 - Bug in :meth:`DataFrame.plot.bar` with ``stacked=True`` where labels on stacked bars with zero-height segments were incorrectly positioned at the base instead of the label position of the previous segment (:issue:`59429`)
 - Bug in :meth:`DataFrame.plot.line` raising ``ValueError`` when set both color and a ``dict`` style (:issue:`59461`)
 - Bug in :meth:`DataFrame.plot` that causes a shift to the right when the frequency multiplier is greater than one. (:issue:`57587`)
+- Bug in :meth:`DataFrameGroupBy.plot` with ``kind="scatter"`` where all groups used the same color instead of different colors for each group like line plots do (:issue:`59846`)
 - Bug in :meth:`Series.plot` preventing a line and bar from being aligned on the same plot (:issue:`61161`)
 - Bug in :meth:`Series.plot` preventing a line and scatter plot from being aligned (:issue:`61005`)
 - Bug in :meth:`Series.plot` with ``kind="pie"`` with :class:`ArrowDtype` (:issue:`59192`)

pandas/plotting/_matplotlib/core.py

@@ -1365,7 +1365,7 @@ def _make_plot(self, fig: Figure) -> None:
         # if a list of non-color strings is passed in as c, color points
         # by uniqueness of the strings, such same strings get same color
         create_colors = not self._are_valid_colors(c_values)
-        if create_colors:
+        if c_values is not None and create_colors:
             color_mapping = self._get_color_mapping(c_values)
             c_values = [color_mapping[s] for s in c_values]
 
@@ -1416,7 +1416,7 @@ def _get_c_values(self, color, color_by_categorical: bool, c_is_column: bool):
         if c is not None and color is not None:
             raise TypeError("Specify exactly one of `c` and `color`")
         if c is None and color is None:
-            c_values = mpl.rcParams["patch.facecolor"]
+            c_values = None
         elif color is not None:
             c_values = color
         elif color_by_categorical:

pandas/tests/plotting/test_groupby.py

@@ -152,3 +152,52 @@ def test_groupby_hist_series_with_legend_raises(self):
 
         with pytest.raises(ValueError, match="Cannot use both legend and label"):
             g.hist(legend=True, label="d")
+
+    def test_groupby_scatter_colors_differ(self):
+        # GH 59846 - Test that scatter plots use different colors for different groups
+        # similar to how line plots do
+        from matplotlib.collections import PathCollection
+        import matplotlib.pyplot as plt
+
+        # Create test data with distinct groups
+        df = DataFrame(
+            {
+                "x": [1, 2, 3, 4, 5, 6, 7, 8, 9],
+                "y": [1, 2, 3, 4, 5, 6, 7, 8, 9],
+                "group": ["A", "A", "A", "B", "B", "B", "C", "C", "C"],
+            }
+        )
+
+        # Set up a figure with both line and scatter plots
+        fig, (ax1, ax2) = plt.subplots(1, 2)
+
+        # Plot line chart (known to use different colors for different groups)
+        df.groupby("group").plot(x="x", y="y", ax=ax1, kind="line")
+
+        # Plot scatter chart (should also use different colors for different groups)
+        df.groupby("group").plot(x="x", y="y", ax=ax2, kind="scatter")
+
+        # Get the colors used in the line plot and scatter plot
+        line_colors = [line.get_color() for line in ax1.get_lines()]
+
+        # Get scatter colors
+        scatter_colors = []
+        for collection in ax2.collections:
+            if isinstance(collection, PathCollection):  # This is a scatter plot
+                # Get the face colors (might be array of RGBA values)
+                face_colors = collection.get_facecolor()
+                # If multiple points with same color, we get the first one
+                if face_colors.ndim > 1:
+                    scatter_colors.append(tuple(face_colors[0]))
+                else:
+                    scatter_colors.append(tuple(face_colors))
+
+        # Assert that we have the right number of colors (one per group)
+        assert len(line_colors) == 3
+        assert len(scatter_colors) == 3
+
+        # Assert that the colors are all different
+        assert len(set(scatter_colors)) == 3
+        assert len(line_colors) == 3
+
+        plt.close(fig)