Want to shoot photographs of rainbow-colored smoke? Just strap some color gels to your flash(es). Photographer Sean Wyatt used three snooted flashes with two colored gels on each flash to create a rainbow blend of color. He then used the setup to photograph smoke from burning incense sticks.
Here are some of the resulting photographs:
If you don’t have any color gels handy, you can create them yourself using an inkjet printer and a transparency. You can find more of them in this Flickr set.
Image credits: Photographs by Sean Wyatt and used with permission