Ron;
I tried that once as a platoon sgt ...and got some kickback from the troops, especially the black troops. My time was somewhat later than your uncle's, perhaps things changed in the intervening years..
Ron; I still would advise you not to call a hardened Army Ranger or Marine platoon sgt "boy"..but it's a free country...at least for a while..
I'm sure that most of the "boys"in your platoon didn't take it in a derogatory way, some people just look to take things the wrong way. The term "boys" was a term of (dare I say it) affection for each other. When I was in VN, our CO would refer to us as his "boys", none of us, of any "racial group" were offended, and believe me we were some mixed bunch.
I think we all just have to remember; times change, people change, things change. I remember one day, when I was working, I noticed that I had picked the habit of speaking to young men that I had stopped for one reason or another as: "son". When I mention it, to a few of the guys (I'm including gals in this "guys" comment), they said I had been doing it for a couple of years. One of the guys even broke my chops, by saying he wasn't even born, when I started the job.
Remember, "good unit = good morale, good morale = good unit". If you served in a bad unit during the VN years, you did have problems of a racial nature. Usually, the problems of a racial nature, were in non combat units. Guys that served in combat units knew that, color/race didn't matter, the only thing that mattered was if the other guy was a good soldier.
On a related note, "Shifty" of "Band of Brothers" fame, died 1/17/11, no mention was made of his passing either. The only reason I know about it was through an email from a friend of mine. Chuck Yeager wrote a short homage to Darrell "Shifty" Powers.
Shifty, RIP, Thank you for your service and God Bless.