For hair that is already naturally or dyed blonde, toning shampoos, conditioners and other products designed to decrease yellow blonde shades will help increase the platinum whiteness of the hair. These products are specifically designed to provide blondes with a means of toning down warm yellow or gold tones in favor of the cooler side of the blonde spectrum, which is more white in appearance.
Color theory principles explain why this is effective. Purple is the opposite of yellow on the color wheel, meaning that these specially developed purple toning products will neutralize yellow and gold tones rather than actually turning the hair purple.
Dark hair will need to be chemically treated with a hair bleaching product in order to appear more white. This chemical process typically takes multiple steps and may not result in an immediate transition from dark to white hair. Toning shampoos, conditioners and dyes are designed for use on blonde hair, so using these products on dark hair that has no blonde tones will likely not result in whitening effects. Although these products are purple and can even be quite dark in color, but they are designed to bring out white shades and, if used properly, will not actually turn blonde hair purple.