Oh and is henna a good idea?
henna is a good idea only if you are not planning on changing your hair color until it grows all the way out. Henna reacts very badly with commercial and professional hair color. I'm a stylist and have seen some weird things happen with Henna. Basically the only thing you can do after henna is go darker, and even then the results can be unpredictable. You can not lighten Henna out of the hair.