allow custom username color for chatLine

user's color (e.g. green for NAT) will be ignore

osu.Game.Tests/Visual/Online/TestSceneChatLineTruncation.cs

@@ -38,10 +38,13 @@ namespace osu.Game.Tests.Visual.Online
 
         private void clear() => AddStep("clear messages", textContainer.Clear);
 
-        private void addMessageWithChecks(string text, bool isAction = false, bool isImportant = false, string username = null)
+        private void addMessageWithChecks(string text, bool isAction = false, bool isImportant = false, string username = null, Colour4? color = null)
         {
             int index = textContainer.Count + 1;
-            var newLine = new ChatLine(new DummyMessage(text, isAction, isImportant, index, username));
+            var newLine = new ChatLine(new DummyMessage(text, isAction, isImportant, index, username))
+            {
+                UsernameColour = color
+            };
             textContainer.Add(newLine);
         }
 
@@ -51,6 +54,7 @@ namespace osu.Game.Tests.Visual.Online
                 addMessageWithChecks($"Wide {a} character username.", username: new string('w', a));
             addMessageWithChecks("Short name with spaces.", username: "sho rt name");
             addMessageWithChecks("Long name with spaces.", username: "long name with s p a c e s");
+            addMessageWithChecks("message with custom color", username: "I have custom color", color: Colour4.Green);
         }
 
         private class DummyMessage : Message

osu.Game/Overlays/Chat/ChatLine.cs

@@ -1,6 +1,7 @@
 // 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 System;
 using System.Collections.Generic;
 using System.Linq;
 using osu.Framework.Allocation;
@@ -18,6 +19,7 @@ using osu.Game.Configuration;
 using osu.Game.Graphics;
 using osu.Game.Graphics.Containers;
 using osu.Game.Graphics.Sprites;
+using osu.Game.Online.API.Requests.Responses;
 using osu.Game.Online.Chat;
 
 namespace osu.Game.Overlays.Chat
@@ -66,6 +68,24 @@ namespace osu.Game.Overlays.Chat
 
         private Container? highlight;
 
+        private Colour4? usernameColour;
+
+        /// <summary>
+        /// if set, it will override <see cref="APIUser.Colour"/> or <see cref="DrawableChatUsername.default_colours"/>.
+        /// Must be set when constructor, otherwise throw <see cref="InvalidOperationException"/>.
+        /// </summary>
+        public Colour4? UsernameColour
+        {
+            get => usernameColour;
+            set
+            {
+                if (drawableUsername != null)
+                    throw new InvalidOperationException("Can't change Username color after DrawableChatUsername created");
+
+                usernameColour = value;
+            }
+        }
+
         public ChatLine(Message message)
         {
             Message = message;
@@ -103,7 +123,7 @@ namespace osu.Game.Overlays.Chat
                             Font = OsuFont.GetFont(size: FontSize * 0.75f, weight: FontWeight.SemiBold, fixedWidth: true),
                             AlwaysPresent = true,
                         },
-                        drawableUsername = new DrawableChatUsername(message.Sender)
+                        drawableUsername = new DrawableChatUsername(message.Sender, usernameColour)
                         {
                             Width = UsernameWidth,
                             FontSize = FontSize,

osu.Game/Overlays/Chat/DrawableChatUsername.cs

@@ -77,7 +77,7 @@ namespace osu.Game.Overlays.Chat
 
         private readonly Drawable colouredDrawable;
 
-        public DrawableChatUsername(APIUser user)
+        public DrawableChatUsername(APIUser user, Color4? customColor = null)
         {
             this.user = user;
 
@@ -92,6 +92,14 @@ namespace osu.Game.Overlays.Chat
                 Origin = Anchor.TopRight,
             };
 
+            if (customColor != null)
+            {
+                AccentColour = customColor.Value;
+
+                Add(colouredDrawable = drawableText);
+                return;
+            }
+
             if (string.IsNullOrWhiteSpace(user.Colour))
             {
                 AccentColour = default_colours[user.Id % default_colours.Length];