The workbench colors live in the two Kestral theme files. Syntax highlighting is inherited from the bundled dark_plus.json and light_plus.json files, based on the VS Code default themes.
If you want to contribute:
Clone the repository
Make your changes to themes/kestral-dark-color-theme.json or themes/kestral-light-color-theme.json
Press F5 to open a new window with your extension loaded
Open the Color Theme picker with File > Preferences > Theme > Color Theme
Test your changes and submit a pull request
Feedback and Issues
If you find any issues or have suggestions for improvements, please open an issue on GitHub.