Red onions (also known as purple or blue onions in some mainland European countries) are cultivars of the onion (Allium cepa), and have purplish-red skin and white flesh tinged with red. They are most commonly used in cooking, but the skin has also been used as a dye.

Deatils:

Red onions (also known as purple or blue onions in some mainland European countries) are cultivars of the onion (Allium cepa), and have purplish-red skin and white flesh tinged with red. They are most commonly used in cooking, but the skin has also been used as a dye.