format:fillColor

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "Payload",
  "type": "object",
  "properties": {
    "sheet": {
      "description": "The sheet name.",
      "type": "string"
    },
    "range": {
      "description": "The target range, e.g. `{\"from\": \"A1\", \"to\": \"B3\"}`. May legitimately arrive \"backwards\", `from` below/right of `to`, normalized before use.",
      "$ref": "#/$defs/CellRange"
    },
    "value": {
      "description": "The fill colour to set, or `null` to clear it.",
      "anyOf": [
        {
          "$ref": "#/$defs/Color"
        },
        {
          "type": "null"
        }
      ]
    }
  },
  "required": [
    "sheet",
    "range"
  ],
  "$defs": {
    "CellRange": {
      "description": "An inclusive rectangle. `from`/`to` may be equal, a single cell.",
      "type": "object",
      "properties": {
        "from": {
          "description": "Top-left cell, e.g. `\"A1\"`.",
          "type": "string"
        },
        "to": {
          "description": "Bottom-right cell, e.g. `\"B3\"`.",
          "type": "string"
        }
      },
      "required": [
        "from",
        "to"
      ]
    },
    "Color": {
      "description": "A CSS colour string, `#ff0000`, `#fff2cc`, `rgb(…)`, a named colour.",
      "type": "string"
    }
  }
}