Thank you!! I'm not a coder and didn't spot the errors, so it was very helpful to have them pointed out. I corrected the errors and checked everything again. New result: Noto Color Emojis still display as blank spaces, but with the revised tagging, Noto Emojis display correctly!
The revised file:
Emoji Test - Ima Pseudonym.epub
The code in Calibre:

And how it appears on my Kobo:
Happy to have this working for now. I will go through the main text and set it up the same way so it will display emojis where they occur.
I'm left with the following questions:
- Is there a way to get Kobo to automatically reference an emoji font, so that it isn't necessary to manually tag all emoji instances in the HTML of a book?
- Why will my Kobo Colour display the black and white Noto emojis, but not the color ones?
I'll keep investigating, and if anyone else looks into it I'd be interested to hear what you come up with. Thanks for the help so far!