generalize the hover code

osu.Game/Graphics/Containers/OsuHoverContainer.cs

@@ -0,0 +1,32 @@
+
+using OpenTK.Graphics;
+using osu.Framework.Allocation;
+using osu.Framework.Graphics;
+using osu.Framework.Input;
+
+namespace osu.Game.Graphics.Containers
+{
+
+    public class OsuHoverContainer : OsuClickableContainer
+    {
+        private Color4 hoverColour;
+
+        protected override bool OnHover(InputState state)
+        {
+            this.FadeColour(hoverColour, 500, Easing.OutQuint);
+            return base.OnHover(state);
+        }
+
+        protected override void OnHoverLost(InputState state)
+        {
+            this.FadeColour(Color4.White, 500, Easing.OutQuint);
+            base.OnHoverLost(state);
+        }
+
+        [BackgroundDependencyLoader]
+        private void load(OsuColour colours)
+        {
+            hoverColour = colours.Yellow;
+        }
+    }
+}