Nice pics RFC. While clams can likely be kept alive under PC, I do not think they will thrive as with under other lighting. I feel people way overestimate what wattage of lighting is to consider. For example, If I have 50 watts of light on a 10 gallon tank, that is 5 watts per gallon, about the same average as 2 400 watt MH bulbs on a 150 gallon. However compare the light production of a 50 watt light bulb to that of a 400 watt metal halide. Night and day (no pun intended). The 400 watt has the proper intensity for the proper metabloic action, while the 50 watt bulb will not. The same watts per gallon does not equal the same lighting intensity. Furthermore, with tube bulbs like fluroescents and pcs, the wttage is distibuted over a larger area. With directional lights (like MH), there is a intensity gradient, where much light will be "focused". I have drastically oversimplified these statements, but the concept applies.
Orion- I do not think we can make those statements you said. We have no idea what this clam has looked like in the past to say if it is hyperextending, or bleaching. I may be, or it may be recovering, or it maty be the natural color and mantle.