Greenish skin – or sprouts – on a potato signal elevated levels of solanine, a bitter-tasting compound that is a natural component of this vegetable. It's best to discard any potatoes that have a greenish tinge or more than one or two sprouts. It would take a lot of solanine to make you ill, but it's best to avoid it. * To flavour potatoes without adding fat, toss a few garlic cloves, onion slices or fresh herbs into the cooking water.