TLDR: Your boss owns copyright in art you create on work time.
Depends - what does the employment contract say about IP created in the course of employment?
Absent any specific terms to the contrary,
artistic work created on "work time" belongs to the employer.
In the case of
bona fide employed hairdressers, that's certainly the case.
In the case of chair-hire hairdressers, i don't know that it's ever been tested in court.
That being said, chair hire is basically sham contracting, so I don't see it being any different.