I'm not a fan of the green on a Gen. I. White/blue is a close second; I don't like the Gen. I stripes at all.
For Gen. II, I'd say sapphire, just because there are a few around here (too common) and I only like black as a dark color. Sapphire isn't quite sinister enough for me. (Note: I have a red Gen. I, so it's not like I can talk when it comes to "common" colors!)
Gen. III, I'd say silver. I've seen a LOT of verts with that color combo. I'd love to see a silver coupe, though...
Gen. IV I haven't seen as many of. For a loud, obnoxious car I like loud, obnoxious colors, so I guess anything subtle (outside of black) would get the thumbs-down. I love the orange and SSG colors!
Disclaimer: All that said, I still agree with the above posts; a Viper is a Viper no matter what and is gonna turn heads. My opinions are mostly based on the cars that are common in our area, and they're just that: opinions.