Fix #130651: Tint tool does not show correct color in header

The issue was that the UI code still used the unified paint settings.
It was decided that in `PAINT_GREASE_PENCIL` mode we don't use
the unified paint settings and always use the settings on the brush.

The fix uses the `brush` as the owner of the `color` property instead
of the unified paint settings.

Pull Request: https://projects.blender.org/blender/blender/pulls/131452

scripts/startup/bl_ui/space_view3d.py

@@ -658,9 +658,7 @@ class _draw_tool_settings_context_mode:
 
         if grease_pencil_tool == 'TINT':
             row.separator(factor=0.4)
-            ups = context.tool_settings.unified_paint_settings
-            prop_owner = ups if ups.use_unified_color else brush
-            row.prop_with_popover(prop_owner, "color", text="", panel="TOPBAR_PT_grease_pencil_vertex_color")
+            row.prop_with_popover(brush, "color", text="", panel="TOPBAR_PT_grease_pencil_vertex_color")
 
         from bl_ui.properties_paint_common import (
             brush_basic_grease_pencil_paint_settings,