When you dye your hair with semi - permanent do you lose your natural hair colour?

If the hair dye is a different colour from your natural colour then, yes.

You would lose your natural colour until it washes out/grows out. -------- semi-permanent colors are usually deposit-only, so the natural color is still left beneath the artificial color. unless you have very light blonde hair naturally, the semi-permanent color shouldn't stain your hair, and the color should come out in a matter of a few weeks with normal shampooing. demi-permanent colors are also usually deposit-only, but stain the hair cuticle. The natural color is still left beneath as well, but the stain is more difficult to shampoo out, and will last much longer before fading away. permanent color actually lifts and destroys the natural color molecules, which are rinsed away. it then replaces the original color with artificial pigment molecules. the natural color will be gone for good and there is no way to get it back until the hair grows out.