There is meaning, though -- it's specifically saying something about the person sending it and how they chose to present themselves.

I don't think there's any value to that though, emojis were more neutral before they added a color skin to it. Instead of reading "I'm happy", now you have a combination of "I'm happy but also white" or "I'm happy but also black", I don't think that belongs here and I don't see any point to that.

If you don't like how they appear, some system setting could be made for changing the overall colours to switch them all to black, white, green or any other colour.

Why in heaven's name should it be a system wide setting? What sense would that make?

The whole feature doesn't make any sense in my opinion anyways. But if people are really sensitive to how emoji appears (a big if in my opinion since emojis are trivial but let's go with it), they could change them in the settings.