A1: add ColourUtil.LerpTowardWhite accent-tint helper

HellionChat/Util/ColourUtil.cs

@@ -102,6 +102,26 @@ internal static class ColourUtil
         return (abgr & 0x00FFFFFFu) | ((uint)newAlpha << 24);
     }
 
+    // Mixes an ABGR colour's RGB channels toward white (0xFF) by factor t in
+    // [0, 1]; the alpha byte is left untouched. A1 hover-sheen accent-tint:
+    // a low factor nudges the sweep toward the element's accent hue without
+    // going fully saturated (effect level stays "subtle"). RGB-only on
+    // purpose -- DrawHoverSheen owns the alpha falloff.
+    internal static uint LerpTowardWhite(uint abgr, float t)
+    {
+        t = Math.Clamp(t, 0f, 1f);
+        var a = (byte)((abgr >> 24) & 0xFFu);
+        var b = (byte)((abgr >> 16) & 0xFFu);
+        var g = (byte)((abgr >> 8) & 0xFFu);
+        var r = (byte)(abgr & 0xFFu);
+
+        var nr = (byte)Math.Round(r + (0xFF - r) * t);
+        var ng = (byte)Math.Round(g + (0xFF - g) * t);
+        var nb = (byte)Math.Round(b + (0xFF - b) * t);
+
+        return ((uint)a << 24) | ((uint)nb << 16) | ((uint)ng << 8) | nr;
+    }
+
     public static uint HexToRgba(string hex)
     {
         ArgumentNullException.ThrowIfNull(hex);