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

{
  "type": "minecraft:crafting_transmute",
  "category": "misc",
  "group": "shulker_box_dye",
  "input": "#minecraft:shulker_boxes",
  "material": "minecraft:gray_dye",
  "result": {
    "id": "minecraft:gray_shulker_box"
  }
}