He employed several hand-colourists who were "home-workers" living in various places around Liverpool and very good they were too. A B&W print would be sent out via the very good tramcar public transport system and returned suitably coloured to his studio the same way in a very short time.
It is a fascinating place where visitors are allowed to handle various stuff while getting a conducted tour. It really takes you back to another era of photography and life that existed pre-World War II although he continued to work after the war.
Well worth a visit and free if you are a member of the National Trust organisation.