As for the blue LEDs, I have heard that using them as nightlights helps cichlid parents keep an eye on their eggs/fry when the nocturnal predators come out.
For those fancy high light LED fixtures with blue and white bulbs, I think that it is intended to help balance the color spectrum, in the real world (outdoors) we get an overwhelming amount of blue from the water molecules etc. Our natural light colors tend to be blue or pink in hue, not yellow, orange, or green as most bulbs tend to be.