Question

As we know different soaps have different colours then why the foam are always white when we rub it?

Answer 1

Regardless of whether the original soap/shampoo 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. Isn’t that a bit strange

Short answer: 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.