One can expect to see some color chance from setup to setup within the same clam, as it adapts to it's new enviroment, but the new setup should be within the range of it's natural conditions.
Like mbbuna said, croceas come from very shallow water, most often. 6500K is ideal for a crocea, or anything from the shallows for that matter. You will get beautiful color from a 10K as well, as it has decent red peaks. When they are hatchery raised, they are shaded. This will reduce the intensity of the light, but not alter the spectrum. They have adapted to living within certain conditions, and do best when they are provided with the conditions thousands of years of evolution have given them.
Note, as this is your only clam showing a change/loss of color, it may only be the first.
ozadars, 10,000K is not very low Kelvin. It's actually towards the top of the natural range most clams will be naturally adapted too. Many, if not all clams will do well under 250W 10k bulbs. Post some pics and that will help people visualize your problem.
skippy2, you should be ok. See above.
And just so everyone is clear, there is no cause and effect relationship between the bright colors in the clams mantle and the intensity of the lighting they are provided. I have VERY bright almost electric croceas in my sand bed and Gold maximas 3/4 the way up my water column.
What I am trying to say is each clam is a unique individual, you cannot expect one to gain color if it is in a good setup, by simply changing to a brighter bulb. It has to have the potential and come from less then ideal conditions to really gain any marked increase in color by changing the enviroment.
So a nice gold/tan/brown maxima/crocea with no blue/green/purple ect. can handle the same lighing a beautiful blue/green/purple maxima/crocea can, and it will not necessarily change it's color. It may change it's intensity, but not necessarily.
Bright color in the mantle is not a necessity either. As you percieve the color of an item as the spectrum of light that item reflects, you can assume that a brown clam can handle more blue light then a blue clam can.
But have you EVER seen a red clam?
Didn't think so.
The zooxanthellae that drive the clam need red for photosynthesis. 20K have almost no red. Saltwater is such a great filter of red light, clams never evolved a resistance to it.
So the logical assumption is no red in the spectrum of the light = not happy crocea.
