I began searching my memories of the Thing's team-ups with African-American superheroes. Sure, he teamed up with Black Goliath and even Brother Voodoo in Marvel Two-In-One. But they weren't that great. Then I saw a visual of the Thing smashing a very powerful sign in 1971 and remembered this issue...
Fantastic Four #119, from 1971, written by Roy Thomas and drawn by John Buscema/Joe Sinnott. In this issue, the Black Panther has been captured in the fictional country "Rudyarda", but you can completely see this is South Africa. The Panther has been captured, and the Thing and Human Torch take a trip over there to bust him out.
The villain of this issue is Klaw, the Panther's mortal enemy since his childhood. However, what really stuck in my memory is this sequence where the heroes see the signs "Coloreds" and "Europeans". At this point in time, the United States is just emerging from the Civil Rights movement, where this type of thing has been abolished. As a kid, I was surrounded by relatives from the South, some of whom were pretty racist.
Comics, or any type of fiction/media that young people are exposed to, can help shape values. Even Alan Moore referred to this in recalling the impact Superman comics had on his youth. While I always had the feeling that segregation was wrong, the ideas expressed in this Fantastic Four comic really helped me secure my opinions of right and wrong.
The writers of the 1960s-1970s Marvel Comics were really progressive for their times. The image of those signs behind smashed is what has stayed in my memory for over 30 years! Nuff said.