onWriteRequest: function(data, offset, withoutResponse, callback) {
     console.log('We got: ' + data); // THIS BIT HERE is where we get data
     if (data == 'red') {
          // Turn on the red light
     } else
     if (data == 'green') {
          // Turn on the green...
     }
     callback(Characteristic.RESULT_SUCCESS);
}