dunno how to solve but i guess trick it by saturating it even morethan its supposed to look and when the render becomes desaturated it will be back to normal
But it´s not possible to saturate more than black, or more than white. That´s the problem. Black becomes dark grey.
Rec 709 as a project setting should not affect output in any way, as it covers the full 0-255 8bit RGB value ranges. They should only get limited when using other profiles and working in other bit-depths.. The only other thing that in my experience might cause color shifts is odd combinations of older Windows Media components with the latest AE. In these cases, the ranges may be misinterpreted. As a last thing, also check hardware acceleration options in your players. Sometimes simply a color otpion introduced by your graphics card can make things go crazy. In any case, I would, as a minor, update Windows Media player to the latest and see, if it helps.