In Windows settings users can make simple combinations of colours and photos.
Yet there is much more potential, when editing .theme files directly. There was a kickstarter project "Customatic", trying to create a theme-editor, but it seems that was given up.
I am looking for a dedicated editor, ideally with a GUI which gives live previews as the file (or theme pack) is being edited.
I am aware that any text editor can be used to edit some definitions but there are many things to be considered. For example how to generate a valid new theme id like this:
My motivation is not to make yet-another pretty-pack (there are hundreds for free download on the MS Store, I know). I need to get an old paid installation of CorelDraw hacked to make it useable on Windows 10. This is about contrast, an aspect not available via Windows Personalization. When I manually tweaked some themes, I badly damaged my Windows (start menu and start button gone). So I would muchly appreciate a dedicated editor with some inbuilt know-how.
If nothing is out there, I would like to find syntax highlighting definitions for .theme files (for mainstream editors like Notepad++ or Sublime Text 3 or Kate). Or more documentation please.
If you want to know more about what is involved, have a look here: This (Microsoft) document discusses the format of Theme (.theme) files.
Although the user who gave me that link states:
... clearly not written for Windows 10 because not all of the attributes are the same, and even then not everything is explained completely