Unwelcome shine, and word?

"Unwelcome Shine," 5" x 5" watercolor

Why are black eyes called "shiners"?
What got me to thinking that way was today's WorldWatercolorMonth daily challenge prompt, "Shiny Things."
In an attempt this month to paint the prompts abstractly, I have to think abstractly. I'm not confident enough to try to painting a hubcap or a fork or a flying saucer that really look shiny.
Thus came the idea for a black eye, a "shiner."
The discoloration of the skin caused by a blow is certainly abstract, even if today's little painting seems too realistic, I reasoned. Painting the wild mix of colors was a challenge and fun. 140 lb. d'Arches cold press paper.
When I wondered why they're called "shiners," I found several possibilities, related to the brilliant and dark colors of bruises.
1. Two of the first I found was not pleasant as it had racial overtones. One source could have referred to African Americans who worked as shoe shine "boys" early last century, putting shines on shoes. Or it could have come from the color of African American skin itself, especially when moist from sweat.
Given white Americans' racial prejudice, I'm afraid this is probably accurate.
2. Another possibility is that in the industrial revolution, a penalty for not keeping machinery shiny could have been a beating.
3. It could also come from just the general shine of brilliant colors from the bruise.
4. The term may have several sources and combinations thereof.
I'm sure there are others. See, every word, and every painting seems to have stories, or lead to them.