Rename the Color singleton to avoid the Qt 6.12 clash

shell/plugins/panels/power/Panel.qml

@@ -88,7 +88,7 @@ Panel {
   }
 
   readonly property color batteryFillColor: {
-    return root.bar ? root.bar.foreground : Color.foreground
+    return root.bar ? root.bar.foreground : Colors.foreground
   }
 
   // Cute agent-flavored phrases shown in the hero status line, rotated on a