Beginning with the 2019.1 release, custom themes are supported. Custom themes give designers control of the appearance of built-in UI elements. The customization options include:
change the colors of icons and UI controls,
alter the borders and insets of UI controls,
provide custom editor schemes,
add background images.
The themes available for download illustrate the creative possibilities.
Theme Plugin Development
Themes can be developed by using either IntelliJ IDEA Community Edition or IntelliJ IDEA Ultimate as your IDE (it is highly recommended to use the latest available version). Both include the complete set of development tools required to develop theme plugins. To become more familiar with IntelliJ IDEA, please refer to the IntelliJ IDEA Web Help.
A theme is one of the plugin types. Its structure doesn't significantly differ from plugins extending IDE behavior, and can be implemented by using one of the supported approaches: DevKit or Gradle. The choice of the development approach depends on the project requirements and developer's experience.
DevKit-Based Theme Project
Developing theme plugins with DevKit is the simplest solution and does not require experience with Gradle or similar build tools. The DevKit project structure is generated by default when an IDE Plugin theme project is created by using the New Project Wizard.
See the Developing a Theme section for the development instructions.
Gradle-Based Theme Project
Developing theme plugins with Gradle requires experience with the Gradle or a similar build tool. It offers the possibility of automating some parts of the development process, like patching plugin.xml file with the theme plugin version and other data, as well as building the plugin distribution on CI servers and publishing it to JetBrains Marketplace.
If your project requires any of the mentioned capabilities, see Developing a Plugin using Gradle for more details.