Turquoise was a catalog color from 1938 to 1951 and 1959 to 1979. This does not mean that Turquoise was only made during these years. I have Turquoise water bottles marked 2002 and 2005. Many colors were (and are) produced even though they are not officially catalog colors.
Turquoise is sometimes referred to as Blenko Blue but serious collectors frown upon this designation. I think Turquoise is one of the prettiest of Blenko’s colors. Everyone should have several. Fortunately, there seems to be a lot of them available. I have owned more than my fair share because Turquoise does not seem to reproduce true on the computer screen. In my early days of collecting I would see a picture of a Turquoise and think that it was something I did not have (and therefore must obtain.) I am able to “see” Turquoise more clearly now through lots of practice. It has been several years since I accidently purchased one of them.