The results showed that the variation of the color display were not significantly corelated with the composition of the photopigments of their zooxanthella.
When a light-photon strikes a pigment, part of the photopigment's structure, known as chromophore, absorbs the energy by temporarily altering its molecular structure in a process called bleaching.
And, to throw in a small twist from genetic evidence, there was a study from 2012 that looked at the evolution of photopigments in the eye that detect color.
Rather than evolving new photopigments, they added an internal filter to some of their green-sensitive cone cells, which cuts out green light and forces those cells to respond only to longer wavelengths like red.