Platform theme colors

There are two default color themes: IntelliJ Light and Darcula.

Use the colors consistently within the default themes. To do so, follow these guidelines:

Icons In the article about icons
UI components
Editor scheme TBD
Charts TBD

UI components

Colors for UI components are specified with color keys. A color key is a name of a color property in a particular component, e.g. ComboBox.background, or a generic color property for several components, e.g. Component.borderColor. Color keys of a combo box

Each key has two default color values: one for IntelliJ Light and another for Darcula. Example: ComboBox.background is #FFFFFF in IntelliJ Light and #3C3F41 in Darcula.

Keys allow creating custom color themes. A custom theme is one of the default themes plus a set of color keys with new values in a JSON file. Example: the High contrast theme is a custom theme based on Darcula. New color values are stored in the JSON file.

See the meanings of the parts in a color key in the key naming scheme.

See a complete list of keys with their descriptions in the JSON files: IntelliJ custom keys, JDK keys.

See the color values for the currently selected theme in the LaF Defaults dialog:

To store color values between theme switching, use a scratch *.theme.json file. This might be useful if you want to test colors before implementing them. See guidelines for the theme JSON structure.

The dialog is available in the internal mode. See Tools > Internal Actions > UI in the main menu or find it with Go to Action.
Some color keys are not shown in the dialog by default because they are loaded at runtime with a corresponding UI component. Open the UI with this component to see such keys in the dialog.
Edit a color in the dialog to preview it in the IDE. The edited color is stored until the theme is switched.

If a color is needed:

Choose a color value for all default themes:
- Try reusing any of the existing colors first. Use the LaF Defaults dialog to see the existing colors.
- If none of them fit, choose two new color values that are consistent with IntelliJ Light and Darcula palettes in hue and contrast.
Choose a color key if a component does not have it:
- Use an existing color key if it fits semantically. Otherwise, a UI component might get an unexpected color in a custom color theme.
- Create a new key if none of the existing ones fit semantically. Follow the naming scheme.

Example:
Incorrect: A new component with a light-blue background reuses Focus.borderColor which has a light-blue color in the default themes. A theme author decides they need a bright focus border and changes the color value for Focus.borderColor. As a result, the new component has a bright background with the text unreadable over it.

Correct: A new component with a light-blue background has its own color key ComponentName.background.

Implementation
Use JBColor.namedColor to set a color key and fallback color values:

private static final Color SELECTED_BACKGROUND_COLOR = JBColor.namedColor("CompletionPopup.selectionBackground", new JBColor(0xc5dffc, 0x113a5c));