Hey crazyspaz, making different color layers of fog would indeed be a neat trick to do. One thing I did notice when I used hand helds and fog in the tank is that all around the beam, the fog glows and blends with the color above and below it. One possible way to make the those "layers" more pronounced would be to close the shutters on the lasers (at least with Laserbtb HL's and PL's) and try to balance the amount of light so you could control glow and the size of the layers. I will be using hand helds tomorrow so maybe I will give it a shot.
SilverFire - your note is much better than a rep, thanks!
Vortish - If you have the funds you should look into a projector. They are totally worth it and there is so much you can do with one. I have sold and had published some of my photography of more normal stuff, but never sold or had published any laser pics. Maybe one day.