Navy blue socks would be better, but black is acceptable. The socks don't show very much. Avoid crossing legs or anything that draws attention to the socks. The idea with a suit is to present a uniform image. The line should be seamless. Matching socks keep that line even. Black is acceptable as long as black shoes are also worn.
You could wear white, gray, tan, mauve, dark brown, or navy brown socks of the exact same color of the suit. I would go with white or gray though, that's probably best.
Wear socks that compliment clothes you have on. If your suit is very dark navy blue, almost a black, you could get away with wearing very black socks and shoes.
With a navy blue suit, the color of the socks which would match the best would be pure white or some light color. But certainly black is not the combination.
