Yes, this is one way of doing it. But what will happen with a barbershop if it become known that one of the barbers refuses to serve black clients? The only reason I hear is "but sex work is a different from anything else". Why? Why should it be different in a country when it is legal?
It is different, and the laws reflect it. Private contractors can often turn down jobs. The category of sex work is even more different than that. The laws recognise the intimate nature of the work and the right of refusal. They dont recognise it for other services, although in the usa religious types want to give business the right to discriminate based on sexual orientation (e.g., not making a wedding cake for a gay couple).

