Far as I can tell, they're all blackies at birth......the color is (it seems) added on over a base coating of black....
Got a deal on a K Code redhead at an estate sale for a buddy at work & when I took out the hex nut sweeps to replace them, under the washer area was pure black clean porcelain.....almost like it was coated with the washer in place, but it just had scraped the red off from use since 1988......look at chip & heat blow-out closely & it always seems there's black under that color......might even make the color a little more prone to chipping & flaking, just a guess......