It's interesting that such a fact has been all but lost to history, especially when one considers how much sense it makes. After all, he made his speech in Detroit right around the time it became a majority-black city. Also, King had, by that time, realized that the struggles of the labor movement were part of an overall struggle for justice, and no city has ever been more emblematic of the American labor movement than Detroit.
It's thus fitting that there's a "Tour de Troit" taking place today. If today's weather in the Motor City is anything like what it normally has at this time of year, I give "props" to whoever rides it.
The name of the ride is kind of funny. The name of the city itself means "strait" in French; Francophone settlers who came by way of Quebec named the then-settlement for "le detroit du lac Erie", which separates it from what is now Windsor, Ontario.
(If you are under-age, or of delicate sensibilities, please skip over everything else in this parenthetical element. The second syllable--"troit"--means "narrow" and is pronounced the way Anglophones pronounce a vulgar term for a part of the female anatomy. In fact, it's believed that British soldiers in World War I introduced the term in to the English-speaking world.)
Anyway, congratulations to everyone who is riding today. And thank you for everything, Dr. King!