Don't panic! These types of spots can be remedied or partly nullified depending on the severity. First try simply rubbing it with your thumb or fingers. If slight, the natural oils in your hand will help soften or dilute a small mark. If you have a large pen mark or greasy food spots promise us you will never use paint thinner or other spot removing chemicals to remove them. Remember, drastic treatment will only make the problem worse by lightening the leather and making the spot even more obvious.
To tackle that big dollop of peanut butter and jelly, salad dressing, puppy slobber, buttered popcorn fingerprints, sticky sauce or "what's that smell? OMG the baby" you said you'd never let, whoops, drop on your cover, apply a damp cloth immediately to remove the offending substance. Let the wet spot dry.
If it’s a small spot try removing oil residue with the light touch of a clean eraser. Don't go wild or you’ll rub too much of the color, leaving that spot different from the rest. For tough jobs, dampen a soft cotton cloth with plain warm water. Rub the spot, then the whole surface, so that the moisture is consistent. It will look mottled at first but should dry just fine. Apply a light coating of Bick 4 or Cadillac Leather Lotion. To the entire cover. The spot may still show but will be blended and less obvious.