gitk: show color preferences on the button instead of the label

When the user goes to the color preferences, the eye is automatically
drawn to the color samples. However, clicking on the sample with the
intent to change it does nothing. Instead, the text label also acts as
a button and must be clicked to change the color.

Turn the color samples into clickable buttons and the text labels into
static text. Use non-themed buttons because their color can be changed
by simply specifying the color properties. (Themed buttons would need
a lot more elaboration.)

Signed-off-by: Johannes Sixt <j6t@kdbg.org>

gitk

@@ -11867,10 +11867,10 @@ proc prefspage_colors {notebook} {
     ]
 
     foreach {uielem colorvar idx label title} $coloruielems {
-        label $page.$uielem -padx 40 -relief sunk
-        ttk::button $page.${uielem}btn -text $label \
+        ttk::label $page.$uielem -text $label
+        button $page.${uielem}btn -padx 40 -pady 0 -borderwidth 2 \
             -command [list choosecolor $colorvar $idx $page $title]
-        grid x $page.${uielem}btn $page.$uielem -sticky w
+        grid x $page.$uielem $page.${uielem}btn -sticky w -pady 1
     }
 
     grid columnconfigure $page 2 -weight 1
@@ -11896,7 +11896,7 @@ proc prefspage_set_colorswatches {page} {
         linkfg    $linkfgcolor \
     ]
     foreach {uielem color} $coloruielems {
-        $page.$uielem configure -background $color
+        $page.${uielem}btn configure -background $color -activebackground $color
     }
 }