Here we test the effect on reef corals of heavily grazed (HG) and macroalgae-dominated (MD) substrata through alterations in reflected light. On shallow reefs in Moorea and Taiwan, the intensity of reflected light was reduced ~20% over MD compared to HG substrata, and its quality was modified through a depressed representation of red light. The effects of these contrasting regimes of reflected light were explored with two series of experiments. First, the photophysiology of Porites lobata and Pocillopora verrucosa on light and dark surfaces was measured at 3-m depth in the Moorea lagoon. Second, mesocosms were used to test for a growth response of Montipora stellata exposed to contrasting regimes of reflected light created under three categories of ambient irradiance mimicking shallow and deep water. For both experiments, the treatment surfaces were created with colored plates simulating HG and MD substrata. In the field, photosynthetic yield (ΦPSII) of P. lobata and P. verrucosa was affected by the substratum reflectance, but the effect differed 3-fold between species. In the mesocosm, growth of M. stellata was suppressed by the darkened surface under conditions simulating a deep-water environment, but the light surface mitigated this effect. We conclude that the reflectance characteristics of the substratum can affect coral physiology in shallow water, and suggest that this affect could represent a previously overlooked mechanism mediating the interactions between reef corals and macroalgae.