Doing colored smoke used to be a bit of a hassle in Houdini but as of version 17 it became easier and here I'm showing it with a density cheat so each color will have a different density, it's nice to see how colors mix.
This is done only on single voxel depth so it's relatively fast to sim, and it also can be used for paint color mixing effect, just push up the resolution and play around with the emitters (pos, shape, densities) and you will be amazed by the outcome.