The worst thing is that there is no selective color plugin for Avisynth, at least that I could find with a lot of googling.
*ahem* ;)
A selective colour filter for Avisynth
Any questions will have to be directed to the author, but by a strange coincidence he and I have never been seen in the same room at the same time...
(it doesn't do "Black", but I - I mean he - might get around to that sometime)
DE