I try to set the background color of a control when mouse is over it. I try to do it via the visual state manager. I was able to get the following code running:
You cannot do it dynamically on a single target, but what you can do is create another target (for example called BorderBackgroundAlt) whose background you can explicitly set to {TemplateBinding Tag} in its declaration.
Then you can have BorderBackgroundAlt collapsed by default, and in your animation frame instead of switching colors, switch visibilities, such that BorderBackground is collapsed and BorderBackgroundAlt is visible.