It appears that the term "chrome postcards" is North American based.
I must admit I never heard of it before this. The word chrome, to me, usually means transparency film. (except Veriachrome Pan which was B&W)
Image manipulation must be as old as photography itself.
I remember Irish postcards from the 1960s/1970s and the colours and sky in the postcards were never like that in real life.
See this before and after sample. Even the white car (looks like a Fiat 124) got new bright yellow paintwork.