Red is the color, chemistry is the game when it comes to avian crossbreeds. Two studies have investigated how some birds can synthesize red ketocarotenoids from yellow carotenoids. One experiment has homed in on the cytochrome P450 enzymes used by a breed of bird produced a century ago by crossing yellow canaries and red siskins. The second study compared common zebra finches, which have a distinctive red beak and mutant zebra finches with yellow beaks to identify the P450 genes. The genetic discovery raises new questions about the role of red pigmentation in birds, which is important for sexual and territorial activity but those enzymes are more commonly associated with detoxification processes in the liver. "Our results, which link a detoxification gene to carotenoid metabolism, may shed new light on the debated honesty of carotenoid-based signals," says one of the researchers, Staffan Andersson of the University of Gothenburg, Sweden.