Use a metal test panel painted with the same base color as the car. Then apply two or three different color flame patterns on it. Most flame jobs involve two or three colors.

The Slow Mo Guys recently posted their rainbow fire tornado, which dovetails two previous pyrotechnic projects. Including a non-rainbow fire tornado and an array of slow-mo multi-colored flames.

Different parts of the artwork burn at differnt rates and with different colored flames, adding to the performance when the poster is burned.