Creating Rich Accurate Rollovers

I have some buttons on a page that I’d like to fade from white to orange. However, if you rollout before the entire fading MovieClip plays, it jumps to the out state. I’d like to have it gently fade out, from whatever point you are in the mC, for a more natural looking rollout. I know this is possible, but I can’t seem to code it correctly.

Anyone have suggestions?