Sapphire was a catalog color from from 1979 to 1989. Sapphire is a dead ringer for Cobalt. To be sure your water bottle is Sapphire, buy one with a Silver Hand label. (If you want a Cobalt water bottle buy one with a New Hand label. The Square B labels could be either color.)
UPDATE: March 7, 2012
I came to a realization yesterday that Sapphire IS Cobalt. How do I know? Sapphire was made from 1979 to 1989. Cobalt “replaced” Sapphire in 1990. Azure , which we know is cased Cobalt was first made in 1985, five years before Cobalt was made. It makes no sense that Blenko would make Cobalt for 5 years just to encase in Crystal, so they must have been encasing Sapphire and calling it Azure. Finally, if Cobalt was a different color from Sapphire, Blenko would have changed the name Azure in 1990 when it changed from Sapphire to Cobalt. So, Sapphire is Cobalt.
Blog Update-November 28, 2013-The above update should be warning for those of you who would apply logic to catalog colors for Blenko. I was utterly and completely wrong. Sapphire started out in 1979 looking more like Peacock or Teal but at some point in the eleven years that Sapphire was made the formula was changed. (Possibly for safety reasons.) I assume that it was earlier rather than later because I have not seen a lot of early Sapphire water bottles. Blenko assures me that the new formula was very close to the formula for Cobalt but not exactly the same. If your Azure water bottle has a raised ridge around the bottom then it is cased Sapphire.