Wolf packs can be placed a few blocks outside of the biome they were meant to be placed in during initial mob generation (I haven't tested mob spawning itself) which sometimes causes them to spawn with the wrong variant.

How to reproduce:

1. Create a default world with the seed -2091359327722066416.
2. Run the command /teleport @s -516.54 71.00 50.80 688.05 11.85
3. Observe the wolf pack generating inside the birch forest in front of you.

Expected result:

Wolves would only be able to spawn in the biomes listed in the 24w10a changelog.

Observed result:

Wolves can spawn outside the correct biomes, becoming pale wolves instead of the correct variant.