Corals will respond to ligth intensity, spectrum and UV
received. A coral contains symbiotic chlorophyll-containing cells called zooxanthellae. These cells use the light to produce the nutrients for the coral through photosynthesis.
If your lighting is more intense than the coral is accustomed to it can (and will) expel zome of these cell to protect itself from the excess oxygen being produced (coral bleaching).
If the light intesity is lower the number of cells will increase along with the amount of chlorophyll within the cells.
Less light = More cells = browner appearance
High light = less cells = lighter appearance. Too much light = bleaching.
Reds and Orange are not visible under daylight but pop under actinic. So the spectrum of light will also alter the color you see.
is damaging to coral tissue so they developed UV
protection that is in the blue, purple, pink range. These are the shallow water sps
corals. As we don't have this intense UBV in our tanks they lose some of this pigmentation.