I wonder if it's an additive that's in the oil - like detergent or something? The only reason I say this is because I've seen additives in fuel turn spark plugs different colors too. Ever pull some plugs to find green or red electrodes?
Yep, there is an additive in the oil. It is called condensation.
![Laugh :laugh:](https://board.marlincrawler.com/Smileys/marlin/laugh.gif)