The dependence of U - B, B - V, and V - I color on V magnitude is examined for ten well-observed T Tauri stars, based on photometry from numerous sources. It is found that the 'color slopes' d(B - V)/dV and d(V - I)/dV, due to variability, differ significantly between stars and tend to be larger for T Tauri stars of later spectral type. Furthermore, when the color slopes are small, the B - V color slope is significantly less than the V - I color slope. All of these results are in accord with the hypothesis that the primary source of large-amplitude brightness variations in T Tauri stars is a changing mix of photospheric regions, hot plage regions, and dark spots on the stellar surface. In addition, the large scatter observed in U - B is consistent with flare-like events.