I played around with some red and blue food-colouring today.
Very cool!
This is very similar to what they used to do in Hollywood for special effects. They would shoot tanks of water laced with food coloring (and other stuff) against a black velvet background and then separate out the colored parts of the image from the background to use for sky effects, etc. I believe the clouds around Devil's Tower in Close Encounters of the Third Kind were produced this way... although they didn't use food coloring for that.
It's lots of fun to play around with that stuff.
--Ron