In the extreme hills biome (gravelly mountains), zombie villagers spawn with taiga clothing. I can also go into creative mode in the same biome and use a villager spawn egg, resulting in taiga-variant villagers. However, if I breed cured zombie villagers or creative-spawned villagers, they will only produce plains-variant villagers. This biome naturally creates taiga-variant villagers so it would make sense if these villagers would go on to breed taiga-variant villagers, not plains-variant villagers.

I double checked villager breeding in a normal taiga biome, outside of the extreme hills. Taiga villagers breed correctly in these areas, producing more taiga-variant villagers.

This affects both realms and non-realm games, in both survival and creative worlds.