I did not say anything about “color.” Look carefully at the photo. Besides the grooving, there is what looks like pitting in the metal and some embedded debris. Almost like the motor sat for a good while without being turned. Moisture of some sort rusting maybe, or rust that acted as the abrasive and cause the grooving. Could be anything really. Polishing a crank that is grooved, even minor grooving, only polishes the high spots. You will not polish those grooves out, particularly using the shoe string method. So then when you measure the journal, you are really measuring for the high spot.
