Add class to select tag of top taxonomy term

Hi there,

I have a jump menu displaying a list of taxonomy terms. I have managed to get it to display like this:

books
-item1
-item2
cds
-music
--item1
--item2

etc

What I would like to do is set the background colour of the top taxonomy term e.g. books,cds to a different colour so they stand out in a long list. If I could place a class on the tag of each top taxonomy term I could do this.

Does anyone have any idea how I can insert a class in to these tags?

Thanks,
Matthew