Paul as a guy who makes his living off of coloring hair I would NEVER EVER recommend 12% peroxide which is 40 vol on a hair piece. This high volume is used for high lift blonde shades for maximum lightening of hair. You need to actually be using a semi or demi permanent color. These color are made to wash out of the hair and are not damaging at all. These colors provide optimum control. The permanent color itself is why the color is going too dark and you are trying to compensate by the 12% but you are creating more issues