Right now I'm particularly thinking of black.
@DZPoker spent a long time looking for a rack before finding one, and I've yet to see one come up for sale in the public view. But I guess that speaks to rarity, not desirability (maybe both!). Whites seem to be fairly common, as well as reds, although shade matching is always a problem when trying to make a rack out of thirty chips here and eighty-five chips there.
A few people are trying to make "skittles" sets (like
this one!), where every player gets a stack of chips in their own color. So for something like that they're trying to get many different colors.
Can't speak for anyone else, but yeah, starburst collectors like pretty colors as much as anyone, so the same colors that are widely in demand will be in demand for starbursts as well. For myself, I'm looking for black (to go with my beautiful whites) plus anything else that my wife says "oooh!" when she sees the pictures.