> If I recall, Red meant bloodletting, White meant teeth, Blue meant haircuts.

I'm not sure that can be right, because I think blue's only used in the USA. (At least, I only see it with blue in emoji; in England they're red and white. Amusing if it is though, and the only still-relevant colour has been lost here!)

Ok here it is...

> In Renaissance-era Amsterdam, the surgeons used the colored stripes to indicate that they were prepared to bleed their patients (red), set bones or pull teeth (white), or give a shave if nothing more urgent was needed (blue).

https://en.wikipedia.org/wiki/Barber's_pole

I thought the barber pole was because shaving involved cutting people up so bad, that the blood soaked rags were hung outside.