YF-15:
Updated with several additional prototypes and their paint schemes.
YF-16:
I debated giving the YF-16 CCV its own image but decided against it since the RCAF evaluated the aircraft without its canards, CCV scheme and all.
YF-17
As far as I can tell, this is the only complete collection of all of the two aircrafts' schemes on the Internet, with a few minor exceptions like the Edwards AFB scheme having a flag at some point. The third row are not actual F-18Ls, but rather the YF-17 as it was being evaluated by several other nations.
YF-18A:
F/A-18A prototypes 1-3 as well as the first TFA-18A prototype. #3 is notable for being the first F/A-18 to land on a carrier.