Not white. Not black. Definitely not leopard-spotted.
Red. I heard this in college, and didn't believe it till I saw it with my own eyes. A white bra shows right through, white being too bright. Black shows as well, being too dark. But red basically vanishes. Has to do with wavelengths: red has the longest wavelength of all visible colors, and therefore gets muted the easiest.
Or something like that. I tried to do a web search on the topic, but when you use strings like "red bra white shirt", you get these "Hi, my name is Heather and I'm 19 and I live in your area and would love to meet you" kind of sites, so at the moment I don't have a website to back this up. Just try it yourselves and you'll see.
I tell you this because I've seen a lot of white bras with white shirts out there. But of course, you folks probably know this already; and, being the snarky lot you are, you're rolling your eyes right now and saying, "Duh, we KNOW. God, you're so condescending!" Hey, just trying to help.
[Edit: I imagine a bra color very close to your skin tone would work fine too. I just don't happen to have such a bra, so I can't say for sure. And red is, like, sexy.]