Aside from avoiding toxins, I think the primary benefit of using any color is to block light. The best light to block is probably UV rays, since it can stress plants. However, it may also increase nutritional value of the fruits and vegetables. So, it's give and take. Blocking infrared may help keep the greenhouse cooler, too, which would be helpful in the summer, in hot areas.
If you use green plastic, you might allow mostly only green light to go through (it depends on the color, which may merely look green, but actually allows other colors through in high amounts, too), which probably isn't going to do a lot for your plants, as others have said.
I don't recommend another color instead of green. Clear is best, in my opinion. It's more like outdoors and allows more light, which is generally a good thing. The only things I would consider blocking are UV rays and infrared, but you can still have a clear greenhouse with UV and infrared filters.
Most plastic probably blocks UV rays already. So, infrared making your greenhouse hot is probably mostly what you have to worry about.
If you can see color normally inside a green greenhouse, then it's letting other light besides green in, which is a good thing, in my opinion. I'm guessing most of them let lots of all colors, besides UV, in.