Are green potatoes unhealthy to eat?

Question

I have been told that green (unripe) potatoes are poisonous and that this is "common knowledge". I doubt there are any chemical properties in these potatoes that could cause any harm. AFAIK, potatoes are only a tuber that grows over time, gaining size to store greater amounts of (the same types of) nutrients.

With fruits, the maturation process makes sense because it's a "strategy" to spread the seeds (when they are ready and not before). Tubers are hidden in the ground, they are meant to store nutrients (as seeds) and not to be eaten to spread any seed (as fruits). However, as a part of the "intention" of not being eaten they may contain chemicals and their density may decrease as the tuber grows, so this could be possible.

Answer 1

Wikipedia's Solanine in potatoes explains why some potatoes become green, and what the poison is:

When potato tubers are exposed to light, they turn green and increase glycoalkaloid production. This is a natural defense to help prevent the uncovered tuber from being eaten. The green colour is from chlorophyll, and is itself harmless. However, it is an indication that increased level of solanine and chaconine may be present.

It's not that the potatoes are "unripe"; for example, new potatoes are edible:

New potatoes have thin, wispy skins and a crisp, waxy texture. They are young potatoes and unlike their fully grown counterparts, they keep their shape once cooked and cut. They are also sweeter because their sugar has not yet converted into starch, and are therefore particularly suited to salads.