Following is from the National Food Safety Database
http://www.foodsafety.org/index.htm.
The entry itself was authored by the North Carolina Cooperative
Extension Service.
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"The green coloring sometimes found on whole potatoes is from
chlorophyll and a compound called solanine. If consumed in large
quantities,
solanine can be toxic. It is concentrated in the skin and tissue just
below the skin in potatoes that have been exposed to light, natural or
artificial.
To reduce the risk to toxicity reactions to solanine, remove the green
portion and enough of the underlying potato so that no green portion
remains. Potatoes should be stored in a cool, dry and dark area.
Solanine is also found in the sprouts. It is not soluble in water or
destroyed by heating."
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