import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.scene.layout.VBox;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

public class ChangeColor extends Application {
    private final Color[] cs = {Color.RED, Color.BLUE, Color.GREEN, Color.ORANGE};
    private int i = 0;

    public void start(Stage stage) {
        stage.setTitle("Change Color");

        Button btn = new Button("Click");
        Label label = new Label("HELLO WORLD! Please change my color!");
        btn.setOnAction(e -> {
            i = (i + 1) % cs.length;
            label.setTextFill(cs[i]);
        });
        VBox root = new VBox();
        root.setAlignment(Pos.CENTER);
        root.getChildren().addAll(btn, label);
        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }

    public static void main(String... args) {
        launch(args);
    }
}