musicle,
Serra is right with what he says. Most of the high power lasers on the market that project full color will consist of red, green, and blue laser diodes. By modifying the power and wavelength of each laser, we can adjust how the colors mix. For instance shooting red and green at the same time will make yellow, however if your green diode is 100mW and your red is 100mW, the yellow will be basically lime-green because the color green (at 532nm) will appear much brighter than a comparably powerful red. Likewise, if you use a 405nm 'blue' diode instead of a more primary 455nm, all your blue mixes like cyan and violet will look dark and harsh. Ultimately, when you mix the red, green, and blue diodes you should get white, but like LEDs, this doesn't really happen in practice. To even get close to a blended white you really have to tinker with the projector's power and source wavelengths (by changing out the physical diodes). Something more for a hobbyist or professional laserist to play with, not so much for a weekend DJ. Aside from driving the price of this laser well out of what I think ADJ would want to ask. Not to break rules and bring up prices here, but I have yet to see a LEGAL full color laser with even 10kpps glavo scanning that's not in the four digit price range. And of course you'd most likely need an FDA variance to even use it at a gig, unless ADJ can somehow work it into the Class IIIR bracket.
In regards to youtube videos, you really can't trust them. Lasers act weird on video. Sometimes lasers look shaky or choppy on video due to the laser's scan speed. Oftentimes the colors aren't completely accurate either. I've seen a video of a green laser that looked white! These are things you really just have to see in person.
Hope this clears some things up!