No, leave it. Find out if it is true that blond people really do have more fun. In the time it takes you to wash your hair 28 times you should find out. Report back her after this most interesting and necessary sociological experiment.
Seriously, though, you probably just got an immense shock when you saw that dark haired person in the mirror. Laugh about it. Invite others to have fun about it. Don't take it too seriously, and if after a week or so, when the novelty has worn off, you can decide if you are going to let it grow out or not.