Lifter galley paint

Oil gets dirty due to combustion byproducts. Not the metal. I suppose for the first few miles 'some' coloration might come from the block/heads but that's a short-lived situation. The 'dirty' color you see in oil, or most any liquid, has to come from particles* of something. There's no way a block or heads is gonna lose that many particles to color oil for very long.

Toilet paper filters are another mistake of years gone by. The oil does stay very clean....but it was well proven that aside from being restrictive, the filtration was too fine and would strip the oil of many of the additives the makers put in.

*As a side note, one of my favorite factoids....something most people don't realize and don't want to know....is that all smells are particulate in nature. All of them.