Tan suits are a subset of brown suits, which typically require brown or oxblood shoes. In general, shoe leather should be darker than the suit the shoes are worn with.
Black shoes should never be worn with tan suits, as they will draw the eye downward to the shoes. Brown shoes are extremely versatile, and can be worn successfully with not only tan suits, but also gray, blue, camel and brown suits. Shoes should not match the suit color exactly; a visible contrast between the suit and shoe color is needed to keep the outfit from looking a bit off. The more casual the outfit, the more creative the shoe choice can be.