According to the Vidalia Onion Committee, their first appearance in Georgia was in 1931 when a Georgia farmer, Mose Coleman, discovered the onions he planted tasted sweet, not hot. His displeasure didn't last. When word spread, sweet Vidalia onions became world famous. All-purpose yellow onions are the most common cooking onions. They are hot, and are the most likely to make you cry while you are cutting them.
Spanish onions are a large yellow onion that is milder and sweeter than most storage onions.
When sweet onions are not available, Spanish onions can be substituted. Red onions are sharp and pungent, but also with a bit of sweetness to them. Their color makes them a beautiful addition to salads, but when cooked their color fades unless lemon juice, wine or vinegar is added. White onions are hot with a sharper flavor than yellows. They often are used in Mexican cuisine.