Previously, skin tones for emoji were left up to the font creator. In practice, this meant that they were usually lime green, neon blue, or Simpsons yellow, all of which are cartoonish enough not to be evocative of any particular real-life skintone.

That's not true, IME -- in several of the popular emoji fonts I've seen that don't incorporate specific "skin tone emoji", most emoji for people that aren't expressly silhouettes are white, except a very small number which are black (in both cases, within the range of flesh tones usually associated with those as races, not cartoonish colors.)

EDIT: This is not true of "smiley face" emoji, but of other emoji representing humans or human body parts.