How to change highlight color?

I like the built-in theme but there’s one issue:
When you highlight a variable name, it also highlights that name everywhere else in that file.
But that secondary highlight is so faint I can’t easily see it. How do I change the color/intensity of that secondary highlight?

See example, I highlighted “product” but the secondary highlight is very faint:

I like using as a GUI to change colors etc in my theme

This is probably what you’re looking for:

Open a theme to edit, you can find this setting in EDITOR > Editor


I thought I’d add to this answer because I also had the same confusion. I recently switched to from VSCode, and even though I had the "editor.occurrencesHighlight": "singleFile" setting enabled in my settings.json file, I couldn’t see any highlights at all. So in the VSCode Preferences I changed the Workbench: Color Theme and Workbench: Preferred Dark Color Theme settings from “Anysphere Dark” to “Dark (Visual Studio)”. There are other color theme settings you can change as desired in the preferences.

So short of it is that the “Anysphere Dark” theme (which I guess is the default?) didn’t have highlights that were visible at all on my monitor, while the “Dark (Visual Studio)” theme did.