yes they are safe. The green comes from the potatoes not being kept in a dark place, they will actually start producing chlorophyll when exposed to light for a period of time. It won't hurt you but it can change the flavor a bit.
I used to work on a pertater farm. We culled the ones that had too much green. Guess who bought them. Companies that make potato chips and instant potatoes. The green won't hurt you but it sometimes has a bitter taste.