ADDITIONAL SYSTEM INFORMATION :
MacOS X, Catalina
openjdk version "14" 2020-03-17
OpenJDK Runtime Environment (build 14+36-1461)
OpenJDK 64-Bit Server VM (build 14+36-1461, mixed mode, sharing)

A DESCRIPTION OF THE PROBLEM :
When the stage of an application opens up it first shows its white background before filling it with the content of the root node. This can cause a flicker. On desktop systems this flicker is very short and hardly noticeable but on slower devices, e.g. mobile devices, it becomes very noticeable. 

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Any application shows this behaviour.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The stage should immediately show the root node of the scenegraph.
ACTUAL -
The window is initially empty / white.

---------- BEGIN SOURCE ----------
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class BugDemo extends Application {

   public void start(Stage stage) {
       VBox root = new VBox();
       root.setStyle("-fx-background-color: orange;");
       Scene scene = new Scene(root, 1000, 800);
       stage.setScene(scene);
       stage.show();
   }

   public static void main(String[] args) {
       launch(args);
   }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Theoretically the application could not use CSS but API to fill the background with a color that more resembles the background color of the root node. This way the flicker is less strong.

FREQUENCY : always