To reproduce:
1. Click button "Set disabled"
The color of the circle will remain. But it is expected to become 40% opacite.

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.HBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

public class BugCircleDisabled extends Application {

    @Override
    public void start(Stage stage) {

        HBox root = new HBox(20d);

        final Circle circle = new Circle(50, 50, 25, Color.BLUE);
        
        Button btnSetDisabled = new Button("Set disabled");
        btnSetDisabled.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent t) {
                circle.setDisable(true);
            }
        });

        Button btnGetValue = new Button("Get disabled");
        btnGetValue.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent t) {
                System.out.println(circle.disableProperty().getValue());
            }
        });
        
        root.getChildren().addAll(circle, btnSetDisabled, btnGetValue);
        
        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);
    }

}