Read the Instructions: Most mistakes are made because people don't, says a Clairol hot-line representative. The single most common error in home hair color is removing the color prematurely. "The chemicals stop working after a certain length of time, so there is little harm in leaving the color on too long. But you will get unsatisfactory results from too short a time." Hair color products purchased at beauty supply stores very often don't come with instructions because they are intended for use by professionals.
Choose the Right Shade: Women often err when identifying their natural hair color, thinking theirs is darker than it really is. This can cause problems when you are looking at the color charts. Colorist Louis Licari says, "The reason people come to salons is for the colorist's eye. It's very hard to judge yourself and what colors work best."
Covering Gray: If your hair is 40% gray or less, a semi-permanent hair color will probably work well. And if you choose a golden or reddish color, your gray hair will work as highlights. If there is more gray hair than any other color, the specialists recommend going to a permanent hair color.
Layers of Processing: Fortunately, hair color is not like oil- and latex-based paints. You can put semi-permanent color over permanent color and permanent color over semi-permanent. You can color over hair that has been permed, straightened, relaxed or bleached. (Of course, that kind of hair is more porous and can absorb color unevenly.)
Hair that has never been colored, permed or relaxed is slick, and color can roll right off the shaft.
The best color results are achieved on hair that has been slightly abused by chemicals or the sun.