I'm not sold that it's the over-saturated color. It may be that your magenta star layer in your timeline (or precomp) is set to "draft" quality.
The stars above have all been created in the same layer. Blue and Yellow looks ok but the magenta has always the jagged edges. I get sharp edges if i change the color to less magenta and more white. It has to be something with the colors. I already tried the effect of broadcast compatible colors or how it sounds but without succes.
My workflow for export / import:
Export in after effects cs 5.5 to QT422 HQ 1920 x 1080
import in premiere cs5.5 in XDCAM EX sequence 1920 x 1080
export to XDCAM EX 1920 x 1080 i 50
Don't think this has anything to do with saturation. The CoDec would handle this, anyway. Rather what I see is simply some unfavorable angle combined with two colors being near each other that represent the two opposite extremes of YCbCr color space. There may be some odd scaling, also, causing softening, but per se there is nothing wrong within what the chosen output format can or cannot do. Sure, it can be improved upon e.g. by choosing slightly different colors and slightly different angles, but you will always have to comkpromise due to the compression.