The conventional wisdom for sock color is that it should transition from your pants' color to your shoes' color. Thus, a light gray suit with black shoes should sport dark gray socks. You can't go wrong with that rule of thumb, but what if you're feeling a little playful?
The leg you see is that of one of my favorite suits, which is kind of...mocha color. It's hard to describe. It has a tight alternating pinstripe in light blue and a sort of goldenrod. I got the suit as part of my Jos. A. Bank Orphan Adoption Program, in which I wait like a vulture for an interesting suit to go on sale at the absolute end of its shelf life and then get it for about an 85% discount off list price. (Never pay more than 40% of the list price on a suit at JAB--but that's a topic for another post.)
I ordered these over-the-calf argyle-pattern socks on sale (~$7 per pair) from Paul Fredrick hoping that they would match the suit. It's hard to tell true color from looking at a promo picture on the Internet. Indeed, alas, the socks' brown proved too light! But after a few minutes' fretting, I noticed that their lighter color was almost identical to the goldenrod pinstripe, and their darker color was a nice transition from mocha to my favorite slip-ons' brown. I like the overall effect.