When should I tell him I like him?

Sounds like you might not even have to tell him, he'll probably come on to you first. It sounds like he's taking the initiate by asking you out and whatnot, and if you keep coming out, he'll begin to think you like him, which will cause him to take the leap and ask you.

if you can't wait that long...

If he becomes more sensual or physical with you, this would be a great opportunity to make it clear to him your feelings. You wouldn't have to say anything, all you'd have to do is accept his advances (physical contact).

If you do want to make your feelings clear (and find out his), then hang out until you get into a heavy atmosphere, then just let him know. Only you can decide whether or not its a good time to ask because we don't know this guy :P

And, even if you're black and he's white, if you like each other, I hardly think it matters :)