Using a permanent color on or bleaching very dry or damaged hair will only increase the damage to the hair; it's a good idea to have a professional stylist handle these processes. If you want to do it yourself, use the gentlest product you can find and do a deep conditioning before you color. Semi permanent and temporary colors are a better choice than permanent. In any event, keep in mind that damaged hair is more porous than normal hair, so it absorbs dyes more quickly. Always do a strand test to get the timing right.