Fix SCBA.

src/Avalonia.Visuals/Animation/Animators/SolidColorBrushAnimator.cs

@@ -13,53 +13,62 @@ namespace Avalonia.Animation.Animators
     {
         ColorAnimator colorAnimator;
 
+        void InitializeColorAnimator()
+        {
+            colorAnimator = new ColorAnimator();
+
+            foreach (AnimatorKeyFrame keyframe in this)
+            {
+                colorAnimator.Add(keyframe);
+            }
+
+            colorAnimator.Property = SolidColorBrush.ColorProperty;
+        }
+
         public override IDisposable Apply(Animation animation, Animatable control, IClock clock, IObservable<bool> match, Action onComplete)
         {
             var ctrl = (Visual)control;
 
             foreach (var keyframe in this)
             {
-                // Return if the keyframe value is not a SolidColorBrush
                 if (keyframe.Value as ISolidColorBrush == null)
-                {
                     return Disposable.Empty;
-                }
 
-                // Preprocess values to Color if the xaml parser converts them to ISCB
+                // Preprocess keyframe values to Color if the xaml parser converts them to ISCB.
                 if (keyframe.Value.GetType() == typeof(ImmutableSolidColorBrush))
                 {
                     keyframe.Value = ((ImmutableSolidColorBrush)keyframe.Value).Color;
                 }
             }
 
-            // Make sure that the target property has SCB instead of the immutable one nor null.
+            // Add SCB if the target prop is empty.
+            if (control.GetValue(Property) == null)
+                control.SetValue(Property, new SolidColorBrush(Colors.Transparent));
 
             var targetVal = control.GetValue(Property);
 
-            SolidColorBrush targetSCB = null;
-
-            if (targetVal == null)
-                targetSCB = new SolidColorBrush(Colors.Transparent);
-            else if (typeof(ISolidColorBrush).IsAssignableFrom(targetVal.GetType()))
-                targetSCB = new SolidColorBrush(((ISolidColorBrush)targetVal).Color);
-            else
-                return Disposable.Empty;
-
-            control.SetValue(Property, targetSCB);
-
-            if (colorAnimator == null)
+            // Continue if target prop is not empty & is a SolidColorBrush derivative. 
+            if (typeof(ISolidColorBrush).IsAssignableFrom(targetVal.GetType()))
             {
-                colorAnimator = new ColorAnimator();
+                if (colorAnimator == null)
+                    InitializeColorAnimator();
+
+                SolidColorBrush finalTarget;
 
-                foreach (AnimatorKeyFrame keyframe in this)
+                // If it's ISCB, change it back to SCB.
+                if (targetVal.GetType() == typeof(ImmutableSolidColorBrush))
                 {
-                    colorAnimator.Add(keyframe);
+                    var col = (ImmutableSolidColorBrush)targetVal;
+                    targetVal = new SolidColorBrush(col.Color);
+                    control.SetValue(Property, targetVal);
                 }
 
-                colorAnimator.Property = SolidColorBrush.ColorProperty;
+                finalTarget = targetVal as SolidColorBrush;
+
+                return colorAnimator.Apply(animation, finalTarget, clock ?? control.Clock, match, onComplete);
             }
 
-            return colorAnimator.Apply(animation, targetSCB, clock ?? control.Clock, match, onComplete);
+            return Disposable.Empty;
         }
 
         public override SolidColorBrush Interpolate(double p, SolidColorBrush o, SolidColorBrush n) => null;