minecraft-assets/assets/minecraft/items/large_fern.json

{
  "model": {
    "type": "minecraft:model",
    "model": "minecraft:item/large_fern",
    "tints": [
      {
        "type": "minecraft:grass",
        "downfall": 1.0,
        "temperature": 0.5
      }
    ]
  }
}