Bright orange coloring suggests that a drake, is getting all his vitamins, particularly carotenoids, such as beta-carotene and vitamin A, antioxidants that can be beneficial to the immune system. “This indicates that his behaviors and genes are good enough for him to recognize and eat the right food, or that his immune system is strong enough to produce bright orange legs,” Omland says. “The female sees this as a very attractive trait to pass on to her offspring.”
Study done by Kevin Omland from University of Maryland at Baltimore County