As long as someone tells Dan sooner than later, I'm happy. When someone points out a contradiction with canon long after the fact, we usually wind up with two or three comics worth of explanation, which usually sidelines the storyline for those strips. But since Susan mentioned her hair dye just last strip, perhaps we can turn this into a one-speech-bubble addition of, "Technically, it's not black, just a very dark blue" and go on with the story instead of throwing the whole she-bang into neutral for a week's worth of strips in a few months.