You coverd your friends highlights with a goldwell demi color 5 and 6 b her hair turned violet brown then used 5g and 6n and now its red you dont know what to do?

Ive worked with Goldwell color for many years. 5b and 6b are very warm colors so they will cover a blonde highlight that hasn't been prefilled, very red. However that line does not make a 5g in permanent or demi so im not quite sure what you actually did use. If it is too red you will want to put an ash over it so i would recommened trying a level six a demi colorance first. No specific time frame ( could be anywhere from two to fifteen minutes depending on her hair porosity and color) you just really need to keep an eye on it. If that still didnt eliminate as much red pigment as you'd like you can try a 5a toner, but this will be very strong and will not need much processing time at all.