LibGUI: Add update() when changing widget color or palette

Author: https://github.com/SpencerCDixon
Commit: 5b79d53c89
Pull-request: https://github.com/SerenityOS/serenity/pull/8234

Userland/Libraries/LibGUI/Widget.cpp

@@ -891,16 +891,19 @@ Vector<Widget&> Widget::child_widgets() const
 void Widget::set_palette(const Palette& palette)
 {
     m_palette = palette.impl();
+    update();
 }
 
 void Widget::set_background_role(ColorRole role)
 {
     m_background_role = role;
+    update();
 }
 
 void Widget::set_foreground_role(ColorRole role)
 {
     m_foreground_role = role;
+    update();
 }
 
 Gfx::Palette Widget::palette() const