When dealing with Spirit, there are two different liveries to expect. This one, and the silver-gray livery. If you look at the right main undercarriage door, you'll notice that it belongs to one of the silver-gray Airbuses.

At some point, the original right main undercarriage door was replaced during maintenance, and the replacement door available, was one belonging to one of the silver-gray birds.

There are times where you'll find little discrepancies like this on various aircraft.