Horses, rabbit, parrot, llamas and sheep generate with default color / variant only

The bug

Some naturally spawned animals always spawn with the default color / variant.

• Horse: white
• Llama: creamy
• Sheep: white
• Rabbit: brown
• Parrot: red

Spawning them using spawn eggs or /summon is not affected. Apparently some values are still random, like for example the health of the horses.
Does not affect superflat worlds.