code: function() {
      this.jsonInit({
        "message0": Blockly.Msg.DATA_ITEMOFLIST,
        "args0": [
          {
            "type": "input_value",
            "name": "INDEX"
          },
          {
            "type": "field_variable",
            "name": "LIST",
            "variableTypes": [Blockly.LIST_VARIABLE_TYPE]
          }
        ],
        "output": null,
        "category": Blockly.Categories.dataLists,
        "extensions": ["colours_data_lists"],
        "outputShape": Blockly.OUTPUT_SHAPE_ROUND
      });
    }
docs: Block for reporting item of list.
  @this Blockly.Block