Stay away from white spirit!!!!! it will remove a large majority of the top coat,and quite possibly pull the base dye reet the way through from the flesh side of the leather and that would be fail. If you do use something/anything with any form of solvent be fcuking quick and don't whack it on, Best bet is to try and scratch it off, then rub gently with soap and warm water. Leather is top coated with a water based cross linked PolyUrethane, solvent will remove the finish quicker than a CS bird loses her knickers at FCS.
Oh and when I was a yoof it was rock fall burns in car seats, tip ex WTF?? LOL