This is similar to a problem I had a few weeks ago. It has to do with the way scriptaculous does a highlight:
1) store initial state 2) do highlight 3) restore initial state by setting the element's style attribute
I bet it's storing is a semi-highlighted state, which would be pale yellow.
And (as I found out) step #3 plays hell on your CSS classes.
That said, I don't know how to solve your problem, because I've never done multiple highlights. You might look into scriptaculous' Effects Queues.
Cheers Starr
