Azure was a catalog color from 1985 until 2007. Azure is Cobalt encased in Crystal. Even though Cobalt is still being made in 2012, Azure is not on the menu. My thinking is that when Ocean Blue was introduced in 2008 (Electric encased in Crystal) that it was just too difficult to tell Azure and Ocean Blue apart and that is why Azure was dropped.
(Azure can also be cased Sapphire.)