There's an old thread here somewhere about the color wars; Long story short, NBC winning out over CBS meant that RCA would manufacture most of the cameras, monitors, and other stuff needed to do color, and CBS wasn't about to pay them for the privilege. The other major TV camera manufacturer, Norelco, made color cameras that were at first pretty inferior to RCA's (Their B/W cameras were very good), and once Norelco developed a color camera that was good enough in CBS's eyes (sorry), they finally pulled the trigger on color.
Back to topic, I didn't see the colorized Van Dyke shows, but I do remember watching that reunion show they did, maybe, 10 years ago. The show indicated that Richie owned the Petrie's house, and it seemed like there were a lot of greens in the living room.