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-billed amazon work, "Systema Naturae". The yellow-billed amazon is long. Its plumage is mostly green with pink over the throat, upper breast and sides of neck, and blue in the larger wing feathers. Feathers over the ears are dark blue-green. The bare white eye-rings are surrounded by a narrow rim of white plumage, which continues as a narrow band of white over the forehead. Plumage over the lores is pale blue and the fore-crown is blue. A barred appearance over the back and sides of neck arises from the green feathers having black tips and edges. The tail feathers are green with