"Back in the day"? You still see that one come up with a vengeance every now and again.
Yeah, well when we can no longer brag about current achievements, etc. we revert to reminiscing.
"Back in the day" for me is the 70s, the era of the SOHC4, and I was there.
In the 70s it was becoming the thing to paint engines black, so the conversations came up. I can remember motorcycle magazines with technical articles about it, etc. Like so many things, a non-issue to me.
The factories would often pick up on what the customizers were doing and incorporate them into factory models. Hence the black factory engines late in the 70s.
There were black cylinders on Triumphs and such in the 60s, but they were cast iron, so not apples to apples.
I say paint (or powdercoat-Mystic) whatever you want. If you ride it enough afterwards to indicate overheating good for you.