I am scared it would be bad

I bought new shit to take care of cold tones in my hair. Since I plan the gray hair back I chose it very gray. Hope it will be good, as soon as I know more I could rate it.

It actually says it makes white hair gray, and keep the brown hair good. I am scared of the results, the shampoo is very dark gray but looks nice. I don't want my hair to turn brown. I am impatient to try, but I don't wanna be disapointed. At least, it says it keeps the hair good with a conditioner effect. At least.