On Rollover change tint of movieclip

I have a menu that I want to add some actions on so that when the mouse rolls over each button symbol, a large clip that takes up all of the background changes colour. I could do that with a simple rollover this. but that changes the colour in one sudden stroke while what I’m looking for is a gradual pass from tint A to tint B. As an example, If button A is yellow and button B is blue, it should show the pass from green as I switch from button to button. Any ideas? Thanks.