If memory serves chlorophyll B's peak absorption wavelength is right about 460nm, the same output of royal blues. Chlorophyll A peaks at a slightly smaller wavelength, while carotenoids a little longer. There are other peaks as well, but in theory it would make sense that corals could survive without the secondary wavelength's. Pretty sure algae's chlorophyll use the red wavelengths.
Coral color might be a different story though. Usually florescent pigment works like a sunscreen, blocking out the wavelengths that inhibit or impede photosynthesis. The color you see is the color reflected away. So without these additional wavelengths the coral has no need to expend the energy to reflect them away.