To reproduce:
1. Open Custom Color menu;
2. Open RGB tab;
3. Type 0, 0, 0 topdown;

RGB(0,0,0) is black, but you got blue, which is the RGB(0,0,255)

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ColorPicker;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class JavaFXApplication65 extends Application {

    @Override
    public void start(Stage stage) {

        ColorPicker colorPicker = new ColorPicker();
        
        HBox root = new HBox(20d);
        root.getChildren().add(colorPicker);

        Scene scene = new Scene(root, 300, 250);

        stage.setScene(scene);
        stage.setTitle(System.getProperty("java.runtime.version") + "; " + System.getProperty("javafx.runtime.version"));
        stage.show();
    }

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

}