It's easy to make a rainbow of colored flames using common household chemicals. Here's how to do it, plus I've got a video
of the project if you want to see what to expect.
Materials or a Rainbow of Colored Flames
Basically, what you need are chemicals for each of the colors, plus a fuel. Use a fuel that burns with a clean blue flame. Good choices include rubbing alcohol, 151 rum, hand sanitizer made with alcohol, lighter fluid, or alcohol fuel treatment. You can get a rainbow effect by placing chemicals on burning wood or paper, but sodium in these fuels produces a strongly yellow flame, which tends to overpower the other colors.
Set Up the Rainbow
On a fire-proof surface, line up small piles of powder for each of the colorants. Usually you'll run your rainbow red, orange, yellow, green, blue and violet. For me, it works best if I try to keep the colorant chemicals separate. When the fuel is added, some of the colors naturally will run together.
Table of Flame Colorants
||strontium nitrate or a lithium salt
||contents of an emergency flare or lithium from a lithium battery
||calcium chloride or mix red/yellow chemicals
||calcium chloride bleaching powder or mix salt with flare contents
||boric acid, borax, copper sulfate
||borax laundry booster, boric acid disinfectant or insect killer, copper sulfate root killer