The original emojis were white before the yellow and darker tones were added in 2015. Look up Katrina Parrott for the backstory. In short, before yellow was the default, White was the only option, and that’s kinda racist, and was only 9 years ago.
Yellow was simply a neutral addition to emojis that matched well with the existing yellow smiley face (which that French asshole keeps charging people for).
Thanks for questioning your assumptions. Further reading if you’re interested:
https://duckduckgo.com/?q=parrot+skin+tone+emoji+&t=ffip&ia=web
Thank you, I had no idea the first phone emoji characters were a third party add-on. That explains how they got there, since Apple is pretty notorious for not including people shaped things in their art.