All female guppies have a dark triangular area on the back of the female's belly.
Male guppies are brighter colored than females and slightly shorter and slimmer than females.
Cockatiels with yellow faces are always males. Female Canaries chirp, males sing. The most popular pet bird is the Parakeet. The color of a dog's tongue is from pigmentation determined by genetics, not disposition, and varies from breed to breed. Some breeds, like the Chow, always have black tongues, and while Chows have the reputation of being mean, many are not.