The Gouldian Finch, also known as "Rainbow Finch." Scientific Name: Erythrura gouldiae • Adult Size: About 6 inches (15 cm)• Weight: About 0.5 ounces (15 g). They are endangered in their native Australia. Gouldian Finches are found with three head colors: red, black or yellow. Their breasts can be either purple or white and their backs can be three different colors! There are blue backs, yellow backs, and the regular green back.