Colors on HDMI screen turn green on kernel mode setting, tested with 2.6.37, 2.6.38, and 3.0. It definitely worked fine with 2.6.35 and earlier. It renders the display unusable, it is not just a small color glitch. This might be related to HDMI audio misdetection.
This bug was originally filed in freedesktop.org bugzilla¹ and more information from multiple reports can be found there. Since the issue is a kernel bug and this major regression has still not been addressed after half a year, maybe an entry in the kernel bugzilla will move things forward.
I'm seeing the issue on a G35 mainboard (Asus P5E-VM HDMI) and a Sharp LC-46X20E TV, but it was also reported for a HM55-based laptop. I'd be happy to test patches or provide debug output.
*** This bug has been marked as a duplicate of bug 25732 ***