Greens might not work because of the culture,
Green, or "Midori" in Japanese, is in some contexts associated with work for hire. (Translation: prostitution.)
In Chinese, green is symbolic of a cuckolded husband.
In this country, all the dark green Ford Tauruses that were ever built were sold to single men. (Not necessarily gay -- just single.) Next time you're on the road, check it out. ;P
It's funny how this works. White in China is symbolic of death, not life. (For that, you have to go to red.)
I think a lot of people could chime in with cultural/regional/ethnic quirks, but the hardest one I've run into all along is the taboo on greens. So while I'd also like to see a jade-colored Z, I doubt the Japanese could bring themselves to producing one.
(But
there's always Earl Schieb!)