Add AlphaBlend tint mode to TintEffect (#1131)

* Add AlphaBlend

* Update CHANGELOG.md

Author: keveleigh

org.mixedrealitytoolkit.uxcore/CHANGELOG.md

@@ -4,6 +4,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## Unreleased
 
+### Added
+
+* Added `AlphaBlend` tint mode to `TintEffect`. [PR #1131](https://github.com/MixedRealityToolkit/MixedRealityToolkit-Unity/pull/1131)
+
 ### Fixed
 
 * Fixed "leaked managed shell" issue in `UGUIInputAdapter`. [PR #1096](https://github.com/MixedRealityToolkit/MixedRealityToolkit-Unity/pull/1096)

org.mixedrealitytoolkit.uxcore/StateVisualizer/Effects/TintEffect.cs

@@ -132,7 +132,6 @@ public override void PrepareFrame(Playable playable, FrameData info)
                 {
                     ApplyColor(startColors[i], tintables[i]);
                 }
-                
             }
 
             /// <inheritdoc />
@@ -162,6 +161,12 @@ public override void ProcessFrame(Playable playable, FrameData info, object play
                     {
                         targetColor = currentColor * TintColor;
                     }
+                    else if (BlendMode == BlendType.AlphaBlend)
+                    {
+                        // Simulate layering a transparent color over the current color
+                        targetColor = Color.Lerp(currentColor, TintColor, TintColor.a);
+                        targetColor.a = currentColor.a; // Preserve the graphic's original overall opacity
+                    }
                     else
                     {
                         targetColor = TintColor;
@@ -191,7 +196,12 @@ internal enum BlendType
             /// <summary>
             /// Multiply the tint color onto the existing color stack.
             /// </summary>
-            Multiply
+            Multiply,
+
+            /// <summary>
+            /// Alpha-blends the tint color onto the existing color stack using the tint color's alpha value.
+            /// </summary>
+            AlphaBlend
         }
 
         [SerializeField]