Bleu

Axolotl's Blue Variant cannot be inherited! In vanilla, there's a 1-in-1200 (configurable) chance that an axolotl will be blue, this is now the only way they will be blue!

When both parents are blue, the baby may be a random non-blue color. When either parent is non-blue, their variant may take priority. When neither parents are is blue, their baby may be one their colors, uniformly randomly (50/50).

It will likely take many attempts to get blue axolotls now.

Gamerule

"blueAxolotlVariantRarity"
  - Inverse probability of a baby axolotl being blue.
  - minimum of 1    => 100% blue
  - default of 1200 => ~0.083% blue
Set (as an Operator) with "/gamerule blueAxolotlVariantRarity <Integer>".

Icon's Blue-Axolotl done by pandigirl1999.