Keywords should definitely be highlighted. It's part of the structure of the code. Being highlighted makes it very quick to distinguish between keywords and variables and helps readability by making them easier to skim over and jump to. Maybe they could be the same color as punctuation, if number of colors is a problem.
I also like minimal themes (and light mode!) but keywords are precicesly the thing I want highlighted. The "Visual Studio(Light)" theme in VSCode gets it pretty close to what I want but still has some inconsitencies that bug me but I haven't bothered making my own to fix them yet. It primarily just highlights keywords, comments, strings.
But then you can have something like public async Task<byte[]> SomeMethod(DateTime date, int someNumber) and int is highlighted but DateTime isn't...
