IMoO/loot_tables/entities/brown_mooshroom_shear.json

{
    "pools": [
        {
            "rolls": 5,
            "entries": [
                {
                    "type": "item",
                    "name": "minecraft:brown_mushroom",
                    "weight": 1,
                    "functions": [
                      {
                        "function": "minecraft:set_data_from_color_index"
                      },
                      {
                            "function": "set_count",
                            "count": {
                                "min": 1,
                                "max": 1
                            }
                        }
                    ]
                }
            ]
        }
    ]
}