I would think it would be more obvious that green is very "in" at the moment, a lot of corporations are trying to create enviro-friendly images and these type of domains seem to be going up in value as the public view moves more and more on the whole global warming issues, etc... maybe good as an e-store selling purple things? or maybe a blog reviewing/finding cool products in purple? other than that I wouldn't see it worth more than maybe mid $xx to low $xxx. but if you build it up and can get some proven traffic on it, you can probably get a lot more since it's kind of catchy name.