When you use a fox spawn egg in a frozen ocean, it creates a fox as a snowy variant, however, the deep frozen ocean biome does not have such luxury as snowy foxes, as spawning a fox in a deep frozen ocean will result in a default orange fox, where it should spawn as a snowy variant.
This occurs in the most recent prerelease of the game, and is a result of minecraft:deep_frozen_ocean being left out of the spawns_snow_foxes.json biome tag list.