My guess is that there's something going on with your IDE install as I'm not seeing that issue, nor have I heard about it from any other users (and not seeing coverage would tend to get a more broad and vocal response).
Here's coverage in light theme in IntelliJ IDEA CE:
And here's the same in dark theme:
I'm happy to look at your idea.log file (Help | Show Log in Explorer/Finder/Files), but I'd recommend that you disable any custom theme plugins you have installed, restart the IDE, and see if things show up properly before doing so. My guess is that either another plugin is messing with the color schemes or the IDE install itself is in a bad state and you'd benefit from an uninstall/reinstall.
Regards,
Scott Wells