Need tags to manage files for historical research

The Tags in Finder are not color-dependent. You can assign a color to a Tag, but you don't have to nor do you need the color.

Select a Tag in the Sidebar and it will show all items with that Tag. The Sidebar only shows a limited number of Tags directly, but there is an All Tags button to list them all.

You can also create a Smart Folder that lists items matching whatever combination of Tags you have assigned.

Finder will show files in iCloud Drive. I don't know about any other cloud storage system.

If you're doing serious research you need more than the Finder. Apps like DevonThink will index your data and offer various enhancements like tagging and excellent cataloging. That's where you need to begin your work:

https://www.devontechnologies.com/apps/devonthink

As tags are an extended attribute on files and folders, as long as you are under the auspices of the Finder, or on iCloud Drive, that tag information remains intact. When you venture to other non-Apple filesystems in other Cloud solutions, you run the very real risk of the tag extended attribute data being stripped from the files and folders.

The above is why I agree with Terence Devlin's suggestion.