The phrase "saddle interior" refers to the color of a car's interior, which resembles the rich, warm shade of brown leather used on saddles for horses. Full definition
Exterior color: brilliant black crystal pearl, interior color: black / new saddle interior, body: sport utility, engine: gas v8 5.7 l / 345, fuel: gasoline fuel,... (car.mitula.us)
Some richer colors are also available, with a lovely saddle interior or a deep burgundy that Buick calls Fig, a notable dose of style that eschews the traditional beige and gray for luxury vehicles. (cars.com)