There is a new IntelliJ IDEA 2018.2 EAP build for you to try. You can download it right now from the website, update to it via the Toolbox App, or use patches for the in-product update if you’re using a previous EAP build.
How about making the Darcula theme even darker? Well, if you are on a macOS, you can now darken the IntelliJ IDEA title bars. Just go to Preferences | Appearance & Behavior | Appearance and enable the Use dark window headers option.