minecraft-assets/data/minecraft/recipe/gray_dye.json

{
  "type": "minecraft:crafting_shapeless",
  "category": "misc",
  "group": "gray_dye",
  "ingredients": [
    "minecraft:black_dye",
    "minecraft:white_dye"
  ],
  "result": {
    "count": 2,
    "id": "minecraft:gray_dye"
  }
}