Approx. weight. USA. USDA Certified Organic. Red onions are milder than yellow onions when eaten raw. They also provide a pleasing contrast in salads and other dishes. Overall, red onions contain a higher amount of antioxidant compounds than other types of onions. They are higher in total flavonoids than white onions and yellow onions are considered to be in the middle. Red onions contain 415 to 1917 mg of flavonols compared to yellow ones, which only contain 270 to 1187 mg. Read more about the benefits of red onions.