How Do I change the color of the top user blocks?

I want the three top user blocks (user1, user2, and user3) to be black, not the electric blue they are at present. I changed the .pngs with top in their name to produce half black blocks, but everything below them remains blue. I've walked through the style sheet a dozen different ways but cannot find any color statement that would give this particular shade of blue. I've added background-color statements to every likely candidate, and still no joy. I've looked through every png in images and still can't find one that remains a blue like that one. I'm guessing that the top png provided a gradient down its length and then merged with a color declaration somewhere, but where that somewhere might be, I haven't a clue. Please help ASAP. I've got a site that looks like an unsolved jigsaw puzzle right now! Thanks.