A "fish eye" can seal the deal for Akro Flinties or Fire Opal types but it's not an absolute requirement, especially for Moonie types, and some CACs can show a weak eye too, I think.
Not too sure if that's fish eye or something else on the blue one, i.e., I'm not sure it's a Flintie or Moonie - does it show that opalescent glow when weakly backlit?