Blue axolotls (dark blue, not aqua) should only be able to exist by breeding two axolotls (source). This is also how it works in Bedrock Edition. However, in Java Edition, when an axolotl spawns naturally in the world, it will have a 1/1200 chance of being a blue axolotl. ...
Unfortunately, blue axolotls don’t spawn naturally in the world, they can only be created by breeding two adult axolotls, or by using commands, cheats, or creative mode. The chance of a blue axolotl spawning from breeding axolotls is 0.083%, meaning that out of every 1200 baby axolotls bor...