I think it's cute when some accessories match like earings and purses maybe even your eye shadow, nail polish can be a nifty tool to bring out the colors you are wearing. It doesn't have to match though.
Red nails with blue flip flops are a bit opposite.. unless you are trying to patriotic! (If you live in the U.S.)
It's not that big of a deal if they don't match soo I say - Yes. It is okay!
