This is a highly personal decision. In the past, I stuck to the rule of only wearing black shoes with black, gray, or blue slacks/suits. Recently, with the addition of some great E Green and J M Weston shoes in cognac brown, I've taken the leap to wearing them with blues and the even the (very occasional) gray. Still, I would draw the line at wearing them with black, as I think the contrast would be a bit too much. I think what they look best with is a function of how dark the tan is; I've seen it varying from a light and somewhat yellowish tone to a much darker brown, perhaps even with a bit of a reddish tone mixed in. I like the darker tone myself, and I've even darkened up with polish some of the lighter tan shoes I own. I think the tan color looks very good with khaki, dark brown, olive, and pretty much any other earth-tone. They also can look good with somewhat lighter or faded denim. I think black looks worst, followed by darker gray, then lighter gray. I don't like too much of a contrast between my shoes and my pants; plus, if you wear a belt to match your shoes, a high contrast combination introduces a more jarring look not only on your feet but also at your waist. Of course, the Italians wear their tan shoes with pretty much anything, and some observers would claim this is the height of style, so to each his own.