minecraft-assets/data/minecraft/recipes/black_bed_from_white_bed.json

{
  "type": "crafting_shapeless",
  "group": "dyed_bed",
  "ingredients": [
    {
      "item": "minecraft:white_bed"
    },
    {
      "item": "minecraft:black_dye"
    }
  ],
  "result": {
    "item": "minecraft:black_bed"
  }
}