If DTV cannot figure it out - PM me, I do this type of work on the side... re-align satellite dishes after DTV has been out. I am surprised at some of the so-called "installers" out there... a good portion of them are REALLY good, but I seem to be finding a band of rogue idiots putting DTV systems in and I have re-aligned probably 15 or so dishes.
Normally you would get a pixelated signal (picture broken into little squares) if you get a bad signal with DTV - never seen DTV go B/W - DTV is digital so it would be pretty hard for that to happen... an analog over-the-air (OTA) signal can go B/W because the receive signal is so poor the tuner cannot pick-up the color pulse, thus it drops to B/W...
Good luck and let us know how it turns out!