I'm exporting a lossless AVI from AE CS5.5 on a Windows 7 machine and the result looks great.
However, I need a high quality WMV file as well, so I dump the AVI into AME and (for now) use the WMV 720p HDTV HQ preset.
The resulting export is really messing with my colors, though. See attached photo. The larger frame is the correct export from AE...the smaller more blue frame is what AME is spitting out...
If it makes any difference, a direct WMV export from AE yields the same results (strong color variation).
The usual Gamma and color shift issues with compressed footage formats, compounded by more generic issues with color calibration (or absence of same) and how different media formats do handle some things differently... Just add an adjustment layer with an additional color correction to unskew the result.