The objective of this study was to test the effect of light (sand and CCA) and dark (macroalgae) substrata on the photosynthetic efficiency of coral tissues adjacent to these surfaces. The study was motivated by the conspicuous effects of macroalgae in “darkening” the submarine light fields of reefs, an effect we demonstrated through spectral analysis of the light microenvironment using an underwater spectrophotometer. On a shallow reef (6-8 m depth) in Moorea, reflected light intensities were reduced ~20% over macroalgae versus sand, and depleted of light in the 530-690 nm wavelength range. A manipulative field experiment was used to test the effects of light- and dark- colored substrata on the photophysiology of juvenile colonies of Porites lobata and branches of Pocillopora verrucosa. The treatments were created with painted acrylic plates, which quantitatively mimicked the reflective features of sand and macroalgae, and were sustained for 27 d at 6-m depth; the response of the corals was assessed as relative electron transport rate (rETR) using PAM fluorometry. Under these conditions, the mean rETR of P. lobata was significantly affected by the substratum reflectance, and was 15% higher adjacent to the light versus dark substratum. The treatment was also significant for P. verrucosa, but the mean rETR was 52% higher adjacent to the dark versus light substratum, and some bleaching occurred in a few of the corals adjacent to the light-colored substratum. Thus, there was a species x treatment interaction in the rETR response. These results indicate that corals can exhibit strong, within-colony photo-acclimatization to reflected light in shallow water, and suggest that P. lobata is better suited to high reflectance environments than P. verrucosa.