Tweaking gamma for HD shows

[element33]

How would I tweak the gamma for HD shows viewed in SageTV Client on my PC? They look a bit dark. I don't see any gamma settings in Sage and I don't see any tuner-specific settings in the Device Manager. I don't want to change the monitor settings in Win7 ("Display properties"), because the color looks good in other graphics apps. If I adjust the "Video" settings in NVidia's Color Panel, I'd be changing the gamma for all video players, which I don't necessarily want to do.

Hardware:
Graphics: NVidia GeForce GT 230M
Tuner #1: HP ATSC/Analog TV tuner (digital mode)
Tuner #2: AverMedia Hybrid ATSC/Analog (digital mode)

Software:
SageTV 6.6.2.218 in Win7 x64
Video Renderer: Default
MPEG2 Video Decoder Filter: SageTV MPEG Video Decoder
SageTV MPEG Decoder uses DXVA (hardware acc.): Yes
MPEG4 Playback: DirectShow
H.264 Video Decoder Filter
Win7Codecs (Shark's 007) installed