Most of the N. w on the market are from cultured live rock farmed at some depth. The dominant wave lenght where the animal lives would peak at around 470 nm and there would be a fairly sharp reduction in longer wave lengths (oranges, reds and IR). If you use a bulb that is particularly strong in the blues and greens, the animal will look a bit more like it would in its natural habitat. (The new moon lights are too dim, but peak at about the right wave length.) If you keep an N. w. in this type of light, there is a good chance that eventually it will turn a rusty brown - what some people refer to as a red morph. If you keep it in broad spectrum white light similar to what would be experience near the surface, it may turn green.
Roy