Bought a used flat screen TV to replace an ancient model. I hooked the cable box to the area on the back labeled "component" - input is also set to "component", I have sound and picture, but in black and white only. The video settings on the TV don't appear to be the problem. All channels just black and white. Everything worked fine with the old TV, and other TV's are OK.
Do you have anything else that can you can plug into your TV component cable (Red, Blue, Green) jacks to insure the TV is function properly? Is there anything in the TV setup that controls the intensity of each color (if they are all turned down then no color would be coming through, thus giving you black and white)? What happens if you plug in the composite video (yellow) cable between the Comcast box and you TV?