So your haircolor results came out too dark? What happened? Here are a few possible reasons:
1)Some permanent hair color lines such as the Avlon's Moisturcolor line and the Schwarzkopf Igora10 color line (see separate article on Igora10 color) line will deposit darker if left on (processing) for too long. Between a "slow" foiling application time and the full recommended processing time -- timing can get quite long resulting in a more dark and/or intense color. Consider starting foils from the back of the head if you are worried about darker deposits. (Stylist talk here.) Remember lighteners are a totally different ballgame. Lighteners are accelerated lifting agents. Speed is important! But in regards to permanent color, a 45 minutes processing time may need to be shortened to 15 minutes if the application time took 30 minutes from the placement of the first foil or stroke. If you have resistant grey hair, then the longer the processing time; the better the coverage usually. Some professional haircolor lines such as Wella and Goldwell seem to stabilize regardless of how long the processing time.
2) Your natural haircolor plus product buildup could interfere with the haircolor lifting to the desired lightness. If your natural hair is dark, then a lightener may have to be used first then another color to get the true color that you want. A highlift permanent color can work on dark hair in lieu of lightener when desired results are in the brown family.
If you use a permanent box hair color, consider picking a color lighter than what you want. If it goes too light, it is safer to tone down the haircolor than to try to bleach out haircolor that is too dark.
I recommend mild shampoos with sulfates in them for your first shampoo after a color service just to make sure the "bad stuff" is washed out. Then go into your sulfate-free shampoo.