I just noticed the September 2015 issue of Nuts & Volts has, right on its cover, a project to outfit a Commodore PET with color (digital RGBI) output. It requires a PET with the Universal Dynamic PET motherboard, the one that could be switched between 40 and 80 columns via jumpers; the actual output is only in 40 because of memory limitations. The specific project in the magazine allows four 16 foreground and 16 background colors per pixel, but it says the author has also made it output 8-bit analog RGB foregrounds with one fixed background color.
-- Eric Christopherson