It is set in the USA. Mc1 is the North Eastern seaboard.
I know where it is. The colour of NYPD uniforms is not likely to have been a big influence on the design. The only US uniformed police shows airing in the UK at the time that I can remember were CHIPs and Hill Street Blues which had much lighter schemes. Everything in NY was plain clothes detective stuff.
Black matches British Police and carries the Nazi fascist overtones.