A new EAP just landed: IntelliJ EAP 5 (261.21525.39). It brings to Linux a feature that macOS and Windows have had for years: you can now synchronize the IDE theme (i.e. Light/Dark) with OS.
When selected, it lets you pick your preferred Theme and Editor Color Scheme, for Light and Dark OS.
Tested on Arch Linux with KDE 6.6. I guess it should work with most desktop environments.