When I first started keeping clams I started with 175watt MH with 10k Hamilton bulbs; that was perfect for derasa but the blue crocea and maxima faded. I upgraded to 250watt MH with 10k XM bulbs and the color came back on the crocea and maxima but the derasa faded from too much light.
I think all animals have an idea light requirement, anything more or less and color and health suffer.