I have a Swing JButton and I\'m also using the following code for my project:
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
This depends on what you want to achieve.
You could use JButton#setContentAreaFilled passing it false, but you, probably also need to call JButton#setBorderPainted passing it falls
JButton#setContentAreaFilled
JButton#setBorderPainted
You could also change the UIManager's default value for the buttons background
UIManager