A looping color tween? Looped tweens have no end, so I'm not sure how this would work here. Hover over, hover out -- it's a finite operation. If you're trying to do something like hover over -- play some color animation -- hover out -- stop the animation, I would suggest setting it up like so:
UIButton
- Background Sprite
- UIWidget (so you can fade this in by adjusting alpha)
-- Foreground Sprite (that you will actually have the color tween on, playing endlessly)
So hovering over a button will fade in the widget. Foreground Sprite will have an active color tween on it the entire time, and you won't be touching it.