Don’t leave it on too long: I accidentally left it on my dry hair for 30 minutes. My hair felt quite frizzy afterward, and even the Joico K-Pak wasn’t enough to get it back to normal.
Blue shampoo will not have much effect on your gray roots except to perhaps make them look a little brighter against your dyed ends. If you overuse blue shampoo, however, your gray roots might take on a bluish tint.
If you have dyed brown hair that is taking on unwanted brassy tones, you may want to give blue shampoo a try and see if it works for you. For many of us, it does a GREAT job!