minecraft-assets/data/minecraft/cow_variant/cold.json

{
  "asset_id": "minecraft:entity/cow/cold_cow",
  "model": "cold",
  "spawn_conditions": [
    {
      "condition": {
        "type": "minecraft:biome",
        "biomes": "#minecraft:spawns_cold_variant_farm_animals"
      },
      "priority": 1
    }
  ]
}