While I was playing around with tile grout I realized it could be utilized for foamy, frothy water. A quick experiment showed that mixing it with gloss medium produced a realistic froth.
I am using a Sauterne Spectra Lock Mini-Unit Part C Color Powder tile grout , I don't know what other ones will do. This one works.
The tile grout is mixed in with the gloss medium. Don't worry about the white gloss color it will disappear when the medium dries.