Thanks Graham. The uuidgenerator worked great. That was the missing key in the theme files.

graham.p.heath@gmail.com wrote:

If you rename the file to themeName.plist from themeName.tmTheme, you can open it with Xcode. You should then see a tree with "Root" and under that, various fields.

There should be a uuid field, if not you can add it.

To get the key, you just run "uuidgen" in your Terminal. If that sounds scary, https://www.uuidgenerator.net/ will make you one.