Add basic structure of colour palette

osu.Game/Graphics/UserInterfaceV2/ColourPalette.cs

@@ -0,0 +1,67 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Allocation;
+using osu.Framework.Bindables;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osuTK;
+using osuTK.Graphics;
+
+namespace osu.Game.Graphics.UserInterfaceV2
+{
+    public class ColourPalette : CompositeDrawable
+    {
+        public BindableList<Color4> Colours { get; } = new BindableList<Color4>();
+
+        private FillFlowContainer<ColourDisplay> palette;
+
+        [BackgroundDependencyLoader]
+        private void load()
+        {
+            RelativeSizeAxes = Axes.X;
+            AutoSizeAxes = Axes.Y;
+
+            InternalChild = palette = new FillFlowContainer<ColourDisplay>
+            {
+                RelativeSizeAxes = Axes.X,
+                AutoSizeAxes = Axes.Y,
+                Spacing = new Vector2(10),
+                Direction = FillDirection.Full
+            };
+        }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
+
+            Colours.BindCollectionChanged((_, __) => updatePalette(), true);
+        }
+
+        private void updatePalette()
+        {
+            palette.Clear();
+
+            foreach (var item in Colours)
+            {
+                palette.Add(new ColourDisplay
+                {
+                    Current = { Value = item }
+                });
+            }
+
+            reindexItems();
+        }
+
+        private void reindexItems()
+        {
+            int index = 1;
+
+            foreach (var colour in palette)
+            {
+                colour.ColourName = $"Colour {index}";
+                index += 1;
+            }
+        }
+    }
+}