Blue–green distinction in language being described. For example, "blue" and "green" might be distinguished, but a single term might be used for both if the color is dark. Furthermore, green might be associated with yellow, and blue with black or gray. According to Brent Berlin and Paul Kay's 1969 study "", distinct terms for brown, purple, pink, orange and grey will not emerge in a language until the language has made a distinction between green and blue. In their account of the development of color terms the first terms to emerge are those for white/black (or light/dark), red and green/yellow. The word for blue
Yellow-tailed black cockatoo is a more solid brown-black in the eastern subspecies, while the southern race has more pronounced yellow scalloping on the underparts. The male yellow-tailed black cockatoo has a black bill, a dull yellow patch behind each eye, and pinkish or reddish eye-rings. The female has grey eye-rings, a horn-coloured bill, and brighter and more clearly defined yellow cheek-patches. Immature birds have duller plumage overall, a horn-coloured bill, and grey eye-rings; The upper beak of the immature male darkens to black by two years of age, commencing at the base of the bill and spreading over ten weeks. The lower beak