Palletwood nail stain removal

Ok, so I admit I mess around with pallet wood for some projects, usually courtesy of the big green shed. One thing I have failed to do is successfully remove the black stains in the wood from where the nails used to be. Short of putting a plug in each affected nail hole, is there an alternative? I have tried oxalic acid deck cleaner with no real results. I can live with the nail holes, or I guess use paint as a last option.