I recently swapped out my old Scientific Atlanta for one of the newer Cisco RNG-200 PVRs from Comcast and everything is great except one thing...all that should be black is purple.
I tried another HDMI cable and got the same result.
The display is fine as I tried the XBOX360 and everything is normal
I rifled through the display menus to see if it was set to some errant configuration and everything looked normal.
Comcast tech support retains it's title as the "Helpless Desk". They are better suited to sharpening pencils.