The greenish color sometimes seen on potato skins occurs when the potatoes have been exposed to natural, artificial, or fluorescent lights.  This can also occur if when a potato is growing a crack in the soil exposes the potato to sunlight.  This is mostly discovered before being sold.

Greening happens a lot more than it used to because supermarkets are often open for longer hours so their displays receive more direct light.  However, it can also happen at home if you store your potatoes out in the open where they are exposed to light.

The green color on the potato is chlorophyll developing in the skin and along with this change, increased quantities solanin is also formed.  Solanin is part of the flavoring complex that gives the potato its taste.  This is concentrated close to the potatoes surface and is easily removed when peeled.  Only if the potato has prolonged exposure to light will the bitter taste and color penetrate deeper into the potato.

We recommend that you don’t eat the green part of the potato because of its bitter taste.  Just peel away the green sections before preparing the potatoes and serving to your guests.