Thanks, hopefully that will get me going again.
Forgive me for a little rant, but I consider it a gross oversight if the current Avisynth can't perform such a simple, basic task internally. Furthermore, I think it's an embarrassment if the "HSIAdjust" filter was removed unnecessarily without a suitable replacement filter in place. (To be fair though, I still don't know for certain that "HSIAdjust" supported RGB...)
A humble plea to the developers: Any chance the "Tweak" filter will support RGB in the future?