Whenever I dye my hair, it washes out within about 2 weeks. Its really annoying. My hair is a light brown, but I dyed it dark brown - And it washed out in about a week. It does this every time, but I dont have the money to have my hair dyed by a hairdresser, as my hair is really thick. Which is the best dye to use? Also, whats the best temperature to wash my hair at?