QT is not the best when it comes to interpret color- there are quite a few posts here regarding this issue. I suggest rendering to an uncompressed format or ProRes if you're on a mac. For web or final delivery use Adobe Media Encoder to compress to h264 or other formats.
Re: Dull collors by Darby Edelen on Sep 28, 2011 at 6:13:39 pm
[Tim Monaghan]"When I render as an animation compression and view in quicktime the colors are so dull in QT."
Are you using a color managed workflow in AE? What color profile is your display using? QT sometimes makes assumptions about how to interpret colors and I wouldn't necessarily trust it.
Where is your final deliverable going to be viewed? You should check it in something that closely resembles its final viewing environment. If it's online video then there may be some options for adjusting the colors within AE to match what QT player is assuming.