ive had like 9 colors in my hair at once(i ahve pics on my profile) the only problem is the colorrs bleeding onto other colors or whatever which sucks, but i didnt have that problem when i used manic panic, ive only had that problem with punky color..
what i did basically was do like 3 colors at a time i basically jsut grabbed chunks, got the dye on them then tin foiled them till they were ready to wash out and then repeat with the other colors