Call your local cable company and ask them for a channel number you can use for a locally generated feed. This is quite common in some communities where they modulate a security camera from a gated entry on to the cable system for the neighborhood. Don't accept channels 95-99 as an option as your DISH receiver won't modulate to those channels. Once you have a clear channel number in your system, set your receiver output to that channel and use a splitter to combine the two to the TV set.
As for the black and white picture, it sounds like they are tuning the TV to the channel first and then pushing the AB switch. Some crappy TVs will stray from the correct frequency when no signal is present, then they don't tune back to it when the signal becomes present. You turn off the TV and then turn it back on to fix it, or you press the AB switch to direct in the sat feed first before changing channels on the TV.
