Are Green Potatoes OK?
This just means the potato has been exposed to light and has produced chlorophyll (the green color). It is most likely safe to eat, minus the green areas.

Producing the chlorophyll also produces solanine, which is toxic in large quantities. Remove the green parts and don't eat more than 4lbs.

For detailed information, see this link.

http://www.wisegeek.com/are-green-potatoes-poisonous.htm