Currently thinking about upgrading the Voyager VOM-78 B&W system. It may be a while, though did ask ASA/Voyager about using the in place wiring, here's what they said. Be interesting to hear if anyone converted to a color system using the existing wiring.
The extension cables that run through the coach for the rear and side cameras can be used still - no need to run new wire. The monitor can be replaced but if you use the existing cameras and they are black and white, the image will be in black and white. There are adapters needed when replacing - that part is OCA85E.
Our friends at RV Cams, https://www.rvcams.com/
specialize in retrofitting older systems with new. Please reach out to them at 877-378-2267 and they will be able to help with the new install of either the monitor, cameras or both.