Just providing an update.
On a fresh Ubuntu 19.04 VM sriram is right, Brave and Chromium both show monochrome emoji.
I was able to fix both Brave and Chromium by closing both browsers and running:
sudo apt install --reinstall fonts-noto-color-emoji
But I don’t understand why that fixes them, so I’m not satisfied.
First of all, why on my host machine is Chromium displaying color emoji but Brave isn’t. I would expect them both to work or both to fail. Granted, I haven’t applied the “fix” to it yet, but I would like to understand how it’s even possible for only one to succeed when they both pull from the system fonts.
Second, what is it about reinstalling the noto font that fixes it. I doubt the files are being changed (though I haven’t checked yet), so I’m leaning toward something in the fontconfig triggers. But the output of “fc-list -v” and “fc-cat -v” is unchanged before and after the reinstall. I probably don’t have a good enough understanding of fontconfig to figure this out at the moment, but hopefully I’ll find time to dive deeper if no one else beats me to it.