Why is, no matter the color of the shampoo, the foam is always white?
The reason your foam stays white even when you use a colored shampoo is because there are small particles in the shampoo that are designed to float around and trap air bubbles. These particles cause the bubbles to be big enough that they reflect light instead of absorbing it, making the foam look white.

If you want to get rid of the whiteness, you can try using a gentle hand with the shampoo and water, or try adding some conditioner to help break down the particles and create smaller bubbles. You may also want to consider switching to a more natural shampoo made without harsh chemicals that could be causing the problem.