I have an HP deskjet color printer that only prints in black and white from my mac ... how do I get it to print in color

Check the printer itself. Some printers you need to set the color & B&W settings on the printer itself instead of the Mac. If that is not the case w/your printer, contact HP tech support and/or post in their forums if they have one.

HP Support

This is the answer for me. You have to turn on colour *on the printer itself*. Yes that's right, everything is controlled from the Mac except the one thing that you would expect to be controlled from the Mac.

UPDATE. Turns out that wasn't it. Can copy in colour. Print diagnostic test is fine. Just won't print in colour.

!Accidental discovery!connect the printer to your mac using the USB cable to get color printouts. After slogging it out in settings,printer settings etc etc this seemingly dumb move solved my problem. Works 100%