So when white people have emojis available that more accurately reflect their skin tone than the neutral-yellow one, and yet they prefer to use the one that DOESN'T reflect their skin tone nearly as well, to me that's pretty strong evidence that it is racially neutral, at least in their perception.

And really, when you're talking about perceived racial overtones of emojis, "in their perception" is what matters, isn't it? There's no objective, 2+2=4 truth that we can point to in this particular argument, as there is in some arguments, because it's all about what subtext different people are reading into things. The objective truth is that those pixels are a certain color; the perception of them is subjective, varying from person to person.

And while some people prefer to use emojis that reflect their skin tone (whether it's lighter or darker), others prefer to use the yellow emojis instead of the ones that would better reflect their skin tone. The fact that they chose that color when they had other options available suggests strongly that they are trying to communicate a "skin tone doesn't matter in the context of this communication" message.

You are arguing that the yellow color isn't inherently neutral, but I claim that you are making the perfect the enemy of the good. Even if the yellow color isn't inherently as neutral as it was intended to be, the fact that people are choosing it over colors that would more accurately reflect their skin tone means that it is neutral enough for the purpose.