Question

How do you change the color of the button.

Answer 1

You should you ToggleButton instead of Button

Answer 2

you can use .setStyle

Button button1 = new Button("Button 1");
Button button2 = new Button("Button 2");
Button button3 = new Button("Button 3");
Button button4 = new Button("Button 4");

button1.setStyle("-fx-border-color: #ff0000; -fx-border-width: 5px;");
button2.setStyle("-fx-background-color: #00ff00");
button3.setStyle("-fx-font-size: 2em; ");
button4.setStyle("-fx-text-fill: #0000ff");