Because this attribute is of type Paint, and because the javafx.scene.paint.Color, javafx.scene.paint.LinearGradient, and javafx.scene.paint.RadialGradiant classes subclass this abstract class ...

javafx-multi-scene-fxml runs on Java 11 or above. If you want to run on a version of Java lower that 11, checkout the pre-javafx-11 branch (However, this branch is beginning to diverge).

This happens when a UI component is not properly initialized or added to the scene graph before layout operations occur. [JavaFX Application Thread] ERROR haveno.common.setup.CommonSetup: Uncaught ...

Get to know the JavaFX 2 libraries by way of a practical exercise: refactoring a Swing-based text editor into one that leverages the rich UI features of JavaFX (Part 2).