Dithering, NVIDIA Quadro 1000M, and HP ZR2440w

My new laptop is an HP Elitebook Workstation 8560w. It's sweet and well supported by Debian 6. I also have a HP ZR2440w monitor, also sweet.

For some reason, with the NVIDIA proprietary drivers, version 290.10 with a 2.6.38 backports kernel on Debian Squeeze, when ever I have the monitor connected via DisplayPort, the NVIDIA driver turns on dithering for the external display. This is not what I want.

The HP ZR2440w is an 8 bit monitor, it doesn't need dithering, and with dithering enabled some colors flicker which is very annoying. The built in LCD on the Elitebook is only 6 bits and so dithering can help make it look like there's a wider color gamut.

To disable dithering on my ZR2440w but keep it enabled on the built-in LCD, my "Screen" section of my /etc/X11/xorg.conf looks like this (DFP-0 is the internal LCD, DFP-6 is the ZR2440w, and I have them mirrored so I only use the ZR2440w when it's connected):



With this config, now my ZR2440w is always non-dithered while the internal LCD always is dithered.