What is purple shampoo?

Purple shampoo is a toning shampoo that uses temporary purple stain to neutralize yellow and brassy tones in your hair.

How does purple shampoo work?

Purple pigment is put into a shampoo and is used just like any regular shampoo. The purple pigment neutralizes yellow tones.   On the color wheel, purple is in direct opposition to yellow.  Opposing colors neutralize one another.  Since purple is not directly opposite of red and orange –  those tones will not be canceled by purple – only yellow.  

Can I use purple shampoo on dark hair?

Yes, but it won’t change the tones in dark hair.  Purple shampoo is only helpful on light colored hair.  So, if you are a brunette, the purple pigment will not do anything for you, unless you have highlights.  Purple shampoo will help the highlights in dark hair from turning brassy.

Is there anything I should be cautious of?

Be careful using purple shampoo on very light, overly porous hair.  Very dry hair may grab too much of the pigment turning hair violet in places. If that is the look you are going for – great!  But if it is not…. just wash the hair a couple times with non pigmented shampoo and the unwanted tone should come out.
If you would like to play it safe – I recommend mixing the purple shampoo in with your regular shampoo.  That way you can control how much pigment is deposited in each shampoo