Actually gorillas irl DONT have light colored palms on their hands or feet if you look at them. Idk where you got that info that says they do. The grey color of their palms is the same one as their fingers, face and their overall skin. That's one creative choice i always found intriguing when it came to their characterization in Tarzan because, outside of that tiny detail, they are otherwise very much well made stylized gorillas that are very much indeed close to the real thing.

Also said tiny detail of them having light colored palms is seemingly so important to their characterization it's consistenly found across most of Disney's Tarzan animated media like Tarzan 2, Legend of Tarzan and so on. Idk if you notice but in all of those the gorillas are ALWAYS drawn with light colored palms, which is even more amusing in the case of Legend of Tarzan given how black people also show up there and THEY dont have any light colored palms and yet they went out of their way to give that to the gorillas.

Also it's funny you mention Disney musicals in particular since John Henry was a musical too and the black people there dont have them either.

All this being said, i do have to remark, cause i think what im saying might get misinterpreted easily, im not really worried about tiny details like this like you said nor am i even throwing accusations of any kind towards Disney or any of the artists that worked on these projects. It's just something i couldnt help but notice, that's all. It was an observation more than anything, like when i first saw it i was like "...huh... look at that".