I got the gray on the following parts by using cold blue followed, wet, by tincture of iodine. It will rust up over night. You then scrub back with Lt Gray or green Scotchbrite pads to the color you want. The best gray color is achieved by getting a real good blue color to start. That generally means you have to get all the oil off the part. I find that scrubbing in Dawn detergent and water works the best.
