minecraft-assets/assets/minecraft/models/item/leather_leggings_redstone_trim.json

{
  "parent": "minecraft:item/generated",
  "textures": {
    "layer0": "minecraft:item/leather_leggings",
    "layer1": "minecraft:item/leather_leggings_overlay",
    "layer2": "minecraft:trims/items/leggings_trim_redstone"
  }
}