The Bindings class has a helper function for custom bindings:

// chapter3.other.CreateBinding.java
Bindings.createObjectBinding(
    ()-> btn.isPressed() ? Color.RED : Color.GREEN, // computeValue logic
    btn.pressedProperty()                           // list of observed values
);

And, as a small reminder, let's rewrite this binding once again using the Boolean binding operations we reviewed in the preceding code:

scene.fillProperty().bind(
        Bindings.when(btn.pressedProperty())
           .then(Color.RED)
           .otherwise(Color.GREEN));