Technically, they should all have their hair up in tight buns because ballet is a dance of intense discipline and focus. Even when warming up, ballet dancers should always have loose hair securely tightened because little distractions like loose hair should NEVER get in the way of practicing and perfecting their technique.

I should know; I danced ballet for years.

^Holy shit you are a SNOB.

I was in a ballet company for a few years and agree but wanted to give them distinguishing features.