client_biome files without foliage_appearance and grass_appearance components cause biomes to fall back to incorrect colors

The new minecraft:grass_appearance and minecraft:foliage_appearance components added in 1.21.60.25 preview cause issues for existing resource packs due to a lack of versioning. Resource packs with client_biome files versioned for 1.21.40 now break the grass and foliage color in certain biomes.

Minecraft expects these grass and foliage appearance components for swamp, mesa, cherry grove, and pale garden biomes now. Resource packs created before these components existed now break the grass and foliage in these biomes.

The following images were taken using the attached sample pack on 1.21.60.25. This same pack has no issues on 1.21.51.

This also affects the Timeless Adventures world from the Marketplace.

1.21.51:

1.21.60.25:

To Reproduce

1. Import and apply the sample resource pack in the latest preview:

1. Create a new world.

2. Teleport to a swamp biome.

3. Observe incorrect grass and foliage colors.

4. Teleport to a pale garden biome.

5. Observe incorrect grass and foliage colors.

6. Teleport to a cherry grove biome.

7. Observe incorrect grass and foliage colors.

8. Import and apply the same sample resource pack in the latest release.

9. Teleport to a swamp biome.

10. Observe normal grass and foliage colors.

11. Teleport to a pale garden biome.

12. Observe normal grass and foliage colors.

13. Teleport to a cherry grove biome.

14. Observe normal grass and foliage colors.

Expected Result

The new grass and foliage appearance components are versioned for 1.21.60 client_biome files only, so 1.21.40 files are not broken by their absence.

Observed Result

The new grass and foliage appearance components are now expected in 1.21.40 client_biome files, so existing resource packs (including Marketplace packs) break in 1.21.60.25.

Recommended Fixes

Lock the minecraft:grass_appearance and minecraft:foliage_appearance biome components behind a 1.21.60 format_version. This would prevent old packs from breaking due to components which did not exist when they were created.

Alternatively, provide the correct fallback values for these biomes so they do not break when the components are missing.