Video Copilot posted another workaround that's been kicked around for well over a year to fix the QuickTime gamma wash out; you'd need QT Pro though:
After rendering into a QuickTime/h.264 file, open it up in QuickTime and select “Show Movie Properties.” Highlight the video track then click on the “Visual Settings” tab. Towards the bottom left you should see “Transparency” with a drop-down box next to it. Select “Blend” from the menu then move the “Transparency Level” slider to 100%. Choose “Straight Alpha” from the same drop-down and close the properties window and finally “Save.”
Update: More in comments at Video Copilot, "VisualHub users can circumvent the problem by selecting “Force: FFmpeg Decoding” when compressing H.264 material. StaxRip and MpegGUI are great Windows H.264 encoding solutions that also don’t exhibit the issue on files they produce." ...and... from Geoffe "Now what I have found certainly does work is export the Quicktime as a 100% Motion-JPEG encoded movie, and then from Quicktime Pro export that as h.264. This looks pretty much just like the original (gamma-wise)." The Animation codec would work too.