I`ve always used creme peroxide which is the catalyst which is mixed with the actual colouring paste... then applied it to system hair..never damaged it. I don`t quite `follow` how you have ended up with two different colours of hair on your system ? [blonde and brown] You initially said you`d simply gone too `deep` with a colour and needed to lighten it again...... from your last post there I see you want all the hair to be a brown colour..... the blonde hair should take on /be easily changed to brown.... I`ve always found `koleston perfect` and creme peroxide mixed, give me best results....very very easy to use. http://wella.com/en-EN/koleston.aspx
You can normally order these off Amazon. I find it hard to get a true idea from these colour-chart things of what shade would be best to order [ or I should say used to when I was blending my remaining hair and a topper--I`m Fullcap now so it doesn`t arise]
Just had a look on Amazon..this is probably better again..... http://www.amazon.com/s/ref=nb_sb_ss_c_1...x=koleston+
I`d simply order the one you think is what you want/need PLUS their `developer`[Creme peroxide] which is down the page there and `treat`the blonde hair first and see how it goes.....only leave it on/in for a few minutes at a time, rinse out and have a `look`....see how it`s looking compared to the brown part.... if the brown part as it is now is the bit which went too `deep`initially, just treat that first with some creme peroxide to lighten it, then dye the blonde hair to match it.... hope that helps.