I'm waiting as well. At least just up to around Aug 20, which is close to the last day those of us that picked up an iPhone 4 on launch day have to order the free case/bumper.
If nothing else I'll just order the black bumper then. I wish Apple would just announce whether they intend to offer them at all in the case program or if they intend to sell the colored one's later...
Why don't you just get a free something now just to have it on your phone for protection and when the colored bumpers are available, you can get those? Yes, I guess you'd have to pay, but you'd be paying for something you really like.
I am waiting to order my free case. I am hoping Apple adds color bumpers soon. I already have a black bumper on my phone, so I'll just be patient and wait another two weeks to see if Apple adds it; if not, then I'll order one of the cases with the lowest amount of shipping time.