For once in my life I was to have red foam. Cmon Science, step up your game.
Most Helpful Girl
Most Helpful Guy
The color of the shampoo in the bottle is the color of the light that is not absorbed by the shampoo. But foam is made of lots of tiny bubbles, and there is only a thin film of water and shampoo around the bubbles. There isn't much shampoo in the film, it's almost all water. The foam appears white because the bubbles are reflecting all colors about equally. There isn't enough shampoo in the foam to give any color to the foam.4