The change is color is from the reaction of the metal plates to the salt and water. The colors vary by the amount of salt used and the type of water. Those foot baths have no health benefit whatsoever. It is a cheap science trick. The bubbles and flakes of stuff are a chemical reaction also. You are wasting your money. I had one of those treatments too at a street fair. The water changed colors, etc. They then informed me that I had yellow-green color from reproductive organ cleansing. . . funny thing is, I don't have any reproductive organs. Gotcha! The whole thing is a bunch of krap. It's a rip off. Do some research and you will find out that you have been had.