gitk: do not set fg/bg color scheme for themed Tk

Ignore the uicolor preference not just for win32, but also whenever
themed Tk is used. On themed Tk it was frequently only changing the
background of only a few select widgets rather than everything -
and the default uicolor was frequently not the background color that
themed Tk used for its widgets, resulting in a messy looking UI
(mostly light gray, with random widgets surrounded by darker gray borders)

Signed-off-by: Christoph Sommer <[email protected]>

Author: sommer

gitk-git/gitk

@@ -11991,6 +11991,12 @@ proc setselbg {c} {
 # radiobuttons look bad.  This chooses white for selectColor if the
 # background color is light, or black if it is dark.
 proc setui {c} {
+    global use_ttk
+
+    if {$use_ttk} {
+        return
+    }
+
     if {[tk windowingsystem] eq "win32"} { return }
     set bg [winfo rgb . $c]
     set selc black