You don't need the perfect color green, just try to get a shade that nothing the subject has on is the same color (you don't even need to use green, but I think it gives the least color cast and best contrast to human subjects). Then in Final Cut use the Color Key filter and fool around with the settings. As I recall I think you need to select Invert to make it the way you want it.
yeah, it doesn't have to be "green." it could be any color pretty much, the key is to not have any shadows. So that it's evenly light across the whole thing. Then you key-out that color in an editing program.
technically it doesn't need to be green to chromakey, just pick a color, blue is also widely used. make sure it's completely lit so there's no shadows on the background (your shadow is fine if you're in the picture) and make sure you're not wearing similar colors.