If you have to have light during the dark cycle, the theory is green is the least detrimental. Reason being how we (and presumably plants) see light.
The way it works is this. Light has all the colors in it. The reason we see different colors is they are the ones that objects reflect in a particular wavelengths. A red cup is reflecting red light. A blue cup, blue light. A plant, being green, is thought to be least impacted by green light due to it completely reflecting that particular wavelength when exposed to a full spectrum light source. By only providing green light, it won't process that wavelength and the theory is it won't even know you turned a light on.
In practicality, you would have to use LEDs with the proper temperature range to produce true green light. An incandescent party light bulb won't cut it. All the bulb does is tints the full spectrum to appear green, you're still getting other wavelengths. A true green light may not have an impact.
My thoughts on the matter, leave em in the fuckin' dark. Unless it's an absolute emergency or right after lights out or lights on, you don't need to be messing around in there. Seriously, do you want someone coming and turn on a light while you're asleep? Not really, it'll make you a cranky bastard.
Plants are the same way, except it'll just make the chicks drop balls. No one wants a chick with balls, unless that's your thing.
