The answer is not as simple as that, as colours go a true green...

The answer is not as simple as that, as colours go a true green stone is highly rare, prices tend to be less than pinks and blue but more than yellow, there is no set price structure for fancy colours. For a reasonable quality polished one carat stone the price could range from 10K to several 100K.
Unfortunately most green diamonds found have a "green skin" that will be removed when polishing to reveal the true colour (normally white/off white).