With regards to the Blue light, The spectrum of moonlight is filtered, and refracted by the water and the organisms in it to a wavelength of about 460 nm which is very blue. The LEDs used in the picture are Royal Blue Luxeon stars which are rated at 455nm wavelength. I really like the effect ! My Ricordea glows more than the brain. I need to get a good picture of same.
Actually, moonlight on the water surface is near sunlight in spectral character. The water filters reds and leaves blues (effectively)... which means by using a blue lamp, you are actually simulating deeper water (but at the compromise of increased radiance levels).
Exact same effect with using blue halides... it just simulates deeper water.
For a true night viewing light, red LEDs are ideal as many fish don't see reds and it is lost quickly with depth.
Red LEDs are a good idea. I still need to install some resistors to decrease the intensity of the Blue LEDs for night time. Most of the fish goto sleep with the lights on but it is still alittle bright.