I own a mac too! here is the code that will work:
myButton.setBackground(Color.RED);
myButton.setOpaque(true); //Sets Button Opaque so it works
before doing anything or adding any components set the look and feel so it looks better:
try{
UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName());
}catch(Exception e){
e.printStackTrace();
}
That is Supposed to change the look and feel to the cross platform look and feel, hope i helped! :)