According to Slate, all watermelon seeds are safe to eat, but it is best to chew them before swallowing them. When consumed, they are a source of protein.
Slate explains that, in most watermelons, white seeds are not fully developed. Colored seeds, such as black, red, tan or dotted, are mature and are planted to grow new crops.
A ripe American watermelon generally has 200 to 800 seeds, but only about 5 percent are still white, Slate says. Another type of watermelon, typically found in China and the Middle East, has only white seeds. Seedless watermelons appear to have white seeds, but these are actually empty seed coats, which usually cover seeds.