DPS_PAR
Ara,
I tried your background test to the PAR with red to black, blue to black,
magenta to black, and I don't see _any_ banding at all. Nothing.
May I suggest that you may have set your Q-factor or block limits too low and
forgotten about them. Also make sure you are not sending 16-bit targa files to
the PAR with the Render options set to 16-bit accidently.
It's clear there's something not quite right in your setup.