I have had an idea that requires a lot of bottle caps of varying colors. Do me a favor and drink extra beer and save the caps for me. Try not to bend them too much.
Currently really in need of blue and yellow.
while looking through my own collection recently, you're best bet for yellows: newcastle, landshark and some smirnoff has a really bright yellow.
blues: bud light, flying dog, sam adams, newcastle summer (baby blue) and the only one i have with navy blue is odells 90 schilling. unfortunately, i have been collecting for a few years now for my own mosaic styled project so i'm not willing to give any up. but i would suggest finding a bar that has a hopper under their mounted bottle opener, not a lot of places still do that, but some of them are willing to let you take whats in there. best of luck to ya.