Yes it is damaging to your hair, so if you have darker or previously colored hair that is fine, or have hair that is damaged, I wouldn't recommend it. If you have a light shade of brown or blond that is natural, you may be able to use a high lift series that will be less damaging to your hair, however if you choose to go darker afterwards you may not have predictable results.
Yes you can color your hair after you decolorize it, however again it depends on the extend of damage done after decolorizing it. It may not hold color if your hair becomes over processed because of decolorization. There fore before decolorizing, or adding color after decolorizing, it's best to do a test strand to see how well your hair takes it.
If decolorizer is not left on until it reaches desired level you will have to use a toner and results may not be very effective.
at 2:47 AM on Jun. 25, 2010