I've used so many green pies in my shoots because sponsors demanded it. Also dark blue pies, which are harder to get as some suppliers don't have the means to whip them up right. These scenes can be seen at www.pievids.com and www.excessivemess.com These vids sold good so i would have to say green pies are liked.
I tried to use green pies once... They were "Kryptonite pies" for the Supergirl scene in SS52. I didn't make them dark enough, though. Anyway, that scene sold horribly... Not sure if it was the green pies' fault.
Pies can be any color you want, depending on your food coloring. They all start out white obviously. Personally, I'd rather have them change colors naturally using different fillings (butterscotch, lemon, chocolate, etc).
I tend to prefer colours that occur naturally in Piedom - white and yellow with some nice contrasting filling or decoration in red, brown, pink. Green and blue I can live with but they aren't ideal. A guacamole pie would be nice though. I guess I just need to be able to rationalise it.