How to find tagged files/folders using the command line in Terminal?
Solution 1:
The correct command to perform Spotlight searches on the macOS Terminal command line is mdfind.
mdfind "kMDItemUserTags == '<your_tags_here>'"
The list all the kMD codes:
mdimport -A
Solution 2:
Turns out you can do something as simple as:
mdfind 'tag:Blue'
Although this will only work in English locales
See this excellent answer that happens to discuss tags: https://stackoverflow.com/a/30281424/404459