I'm kind of in agreement with Hondo44 here. I would use oiled 0000 steel wool to remove all the sanding mark's I could, removing as little original blue as possible. Wipe down with a clean oily cloth and apply Oxpho-blue cream to the oiled white spots with a Q-Tip, avoiding the original blue as much as possible - it will remove the original blue so keep an oily cloth handy. That will remove some of the sanding scars and spruce it up with a good cold blue that can be easily removed with the same oily 0000 steel wool later if desired. No harm - no foul. Nail polish remover will attack and remove the nail polish on the front sight without attacking the blue. Keeping everything oiled is the trick to touch up cold bluing so the cold blue will blend and not be blotchy. It's just a "touch up" not a refinish.

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Jeb