Schimba background-ul de la butoanele din applet

import java.applet.*;
import java.awt.*;
public class index extends Applet {
Button b_rosu,b_albastru,b_negru,b_verde;
public void init(){
setBackground(Color.ORANGE);
setLayout(new FlowLayout(FlowLayout.CENTER,12,12));

b_rosu=new Button("red");
add(b_rosu);
b_albastru=new Button("blue");
add(b_albastru);
b_negru=new Button("black");
add(b_negru);
b_verde=new Button("green");
add(b_verde);
}

public boolean action(Event evt,Object arg){
if(evt.target instanceof Button){
changeColor((Button)evt.target);
return true;
}
else
return false;
}
public void changeColor(Button b){
if(b==b_rosu) setBackground(Color.red);
else if(b==b_albastru) setBackground(Color.BLUE);
else if(b==b_negru) setBackground(Color.black);
else if(b==b_verde) setBackground(Color.green);
}
}