If your hair's health is toast, there's a limit to how drastically you can change your color. Hair that's damaged from frequent hair-color changes, perms, or copious heat-styling shouldn't be lightened up with bleach due to the risk of breakage. Even dark hair color can do a number on weak hair, since permanent hair coloring products typically contain cuticle-swelling ammonia and drying hydrogen peroxide. If your hair is seriously damaged, think about getting some highlights or trying a temporary coloring product, which boosts hair color without intense chemicals.