One thing to note if you buy one on ebay. The boxes have the name of the shadow as well as a number. The shadow label itself does not have a name and number on the label, just the name. The box for Tres Teal will say: Tres Teal 08. Just thought I would mention that as numbered MAC shadows other than these are FAKES.
BTW, these are really sheer on their own. They definitely need a base or to be applied wet with mixing medium. HTH