On the Color Computer 3, that was how it was recently (late 2009) discovered that one could get 256 colors! By using the 640x192 4 color mode on a composite monitor or television, and using a palette of black, dark gray, light gray, and white, while alternating the pixels properly, the NTSC artifacting takes over; you end up with a 160x192 256 color display.
People have converted various images to the dithering patterns necessary to display them; while I haven't personally seen a real image yet (I don't have my Color Computer 3 system set up currently), the digital photos taken of composite monitors have been amazing to see; they say the actual images are even better. While I have found this to be an amazing discovery, it will always be on my mind as to "what if" it had been discovered back when the system was being sold at Radio Shack (1986-1991).
G'Day Gr0sh.
I just stumbled across this post and forum and you mentioning the 160x192x200 odd color artifact mode. Well the pics you mention floating around were taken from my Ntsc coco 3 model and some others were done by a fellow called PotatoHead.
I think I was the 1st person to actually see the full colors in artifact mode on a coco 3. A friend of mine in Queensland only had a Pal coco 3 unit and Jason was the 1 who scaled down the pics colors and matched them close to what the coco 3 palette would do and show all under Mess emulation in black/white. After this he would send me the pics and files to load them up and view them.
Jason and Potatohead deserve a pat on the back for the work they put into show casing this mode on the coco 3. All i did in the end was run the pics on the coco 3 and take pics off the colors too make sure the colors looked right and if needed tweak the coding a touch. Best thing is all this could be done under basic programming no need to know assembly.
I contacted a former coco programmer letting him know about this artifact mode and the possibilities it has. Mr Dekok ended emailing me back saying it was about time people looked at this quirk in the Gime chip, As he played around with it back in the late 80's or early 90's but never did anything with it as back then most users were using RGB displays.
As a last note. Potatohead on the Atari forums said that out off all the artifact modes used on other computers he has never seen any that come close to the coco 3's artifact mode. And matched with the 6809 cpu any games or apps using it would be a killer game or App.