Ah, once again a chance for me to discharge the huge amounts of info I have collected in my 14 short years of life...
L.A.S.E.R. - light amplification by stimulated emission of radiation
Lasers basically work by using something such as a quartz crystal, powered by high voltage electricity to give off a *bright* flash of light. This in turn stimulates the atoms in a gas / liquid in a cylinder. The cylinder has a 100% reflective mirror at one end and a 95% or so reflective mirror at the other.
The atoms are excited to a higher energy state and give off more photons. These in turn excite other atoms and the ligh inside the tube rapidly increases until it is strong enough to come out of the partially silvered end.
I assume that the colour depends on the substance used in the cylinder. Presumably red is the easiest substance to get hold of. I personally have seen red, yellow, blue and green lasers. Therefore you should be able to get any colour you want.
it would be SO DAMN cool if you could get a smoke screen generator and RGB lasers. To create like, a half mile high AVS visualisation in the sky at night.
*gasp* The concerts of the future are gonna be so great!