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
Ischnura erratica have blue bands dorsally, segments 3 to 6 have narrow yellow rings and there is a large blue dorsal patch stretching from segments 7 or 8 to segment 10. The tip of segment 10 is extended into an upward-pointing forked tail. The female has two colour phases. One is similar to the male but with duller eyes and greenish-blue replacing blue. The other has pale patches on the head, a greenish thorax, and a black abdomen with narrow green rings at the base of some segments. Immature females have dull orange patches on head and thorax. "Ischnura erratica" is native