***Nerd alert, please don't read if you don't want a science lesson.***
This all goes back to our elementary school friend ROY G BIV who reminded us that the spectrum of visible light is red, orange, yellow, green, blue, indigo and violet. Water absorbs the longer wavelengths (red) first so blue does penetrate further than red but the blue light does not contribute much to photosynthesis.
Cookie Absent As you can see in this abstract light at the red end of the spectrum is more available for photosynthesis and the energy needs of the coral. But, to our eyes, the blue is prettier. The blue lights also bring out some of the fluorescent pigments but once again I think this is a limitation of our eyes and not that of the coral and the color of the light that is available to it.
