Lighting could be an issue, but there are other variables. Metals - particularly iron, magnesium and potassium are known to 'bend' the colorful part of *some* corals (the fluorophore, which is held in place by very weak Van der Waals forces.) pH could another factor if the tank is overdosed with Kalkwasser or carbon dioxide. If the coral doesn't fluoresce ('pop'), and it is a non-fluorescent protein (usually pink or purple, but sometimes blue or orange) then low intensity lighting - particularly blue - is the likely cause. A quality PAR meter could tell the tale, but a lux meter is OK if lux-to-PAR conversions are known. On the other hand, M. caps are sensitive to high light and will lose their vivid orange color if exposed to excessive light. Red light, in excessive amounts, will reduce the zooxanthellae density/photopigment content which could affect long-term coral health. Since it is the coral animal that makes the colorful proteins, any thing detrimental to its health could result in lower or even more production of their vivid coloration.
