Most people consider turquoise to be one of the original colors, and call it, as well as red, yellow, ivory, blue, and green the Original Six colors. It was fired from 1937 to 1969, almost the entire original run. It was then reintroduced in 1988 due to it’s popularity, and has not been retired since.
The post-86 turquoise is a little greener.
Sources: ShannonZPhotography, Vintage American Pottery