Adding a skin color, let's say a thumbs-up with a black skin tone, its saying: "this is not just a thumbs-up, its different, it's a BLACK thumbs-up". See how racist it is?
Without knowing anything about the particular person, in what ways a black thumbs-up is different than a non-skinned thumbs-up?
Adding a skin-tone is saying there ARE differences, but any difference you can name are actually prejudices about blacks. What was meant to be a simple "ok", "agree", etc. now is charged with an "I don't think you/others and me are the same kind of humans".
That's why using skin-tones in emojis is actually racist.
