antifreeze questions

[CTDiesel at aol.com]

According to audiquattroparts.com green antifreeze is the wrong stuff for all
Audis.  Does anyone one know about that? They state either blue or red color
is the right stuff.  The dealer sells only blue and red in my area (CO) so
maybe its true.  Currently I have green (phosphate free) in my system (4kq /
vw syncro) for only a few months now.  Does anyone know the reasons behind
the neccessary blue or red?

Thanks
DJ