Here's the low down: avisynth's cnr2 and guavacomb are moderately successful at removing the color artifacts.
Many of these artifacts may be edge enhancement related.
Anyway, during fast motion some serious posterization occurs. It's rare, but so bad I can't use those filters.
I switched to VirtualDubMod's Chroma Noise Reduction filter and it work beautifully. It removes 80-90% of all the colors crawling along edges, interference in small textures, and overall improves the picture without softening it. The artifacts are few, far between, and absolutely tolerable in comparison.
This is the second time I've found VD's filters to be superior to the "recommended" avisynth equivalent (the other is Vdub's Levels filter vs. ColorYUV(off_y=0, gain_y=0) ). And I'm talking quality of output. Avisynth may have the edge on speed, but I'd rather encode slower and have better output.
So anyone else that needs to clean Chroma artifacts: try VDubMod's Chroma Noise Reduction Filter. I set YUV to wide and moved the U and V percentages to about 40%.
Cheers to anyone else that gets use out of the hours I spent toying with this. Screenies will follow (maybe).