Have you ever wondered,why your colored soap always have a white foam?
Regardless of whether the original soap is orange, green, pink, yellow or any other color, you have surely observed that the foam or lather that forms when it’s mixed with water and rubbed vigorously is always white in color. The main reason for this is due to The ultra-thin layer of soap (that’s formed when it’s dissolved with water) is pretty much transparent on its own, but the foam looks white, because visible light gets scattered in multiple directions after passing through several surfaces.
The foam is white because the dyes used to impart color to soaps and shampoos are highly diluted. In other words, they only use a tiny bit of dye to color a soap. When we rub soap in water to make lather, an incredibly micro amount of dye goes into the formation of lather. Thus, there’s little (or almost no) color in the foam to begin with.
Thus,The foam in its entirety looks white because when light enters the soap solution, it must pass through a number of tiny soap bubbles, i.e., a number of surfaces. These countless surfaces scatter the light in different directions, which makes the foam/lather look white.
NJC 