case 0: //Yellow
                        Log.d("t", "yellow");
                        button_on = false;
                        yellow.setBackgroundResource(R.drawable.yellow_on_button);
                        new Thread(new Runnable() {
                            public void run() {
                                SystemClock.sleep(500);
                                button_on = true;
                            }
                        }).start();
                        while(!button_on);
                        yellow.setBackgroundResource(R.drawable.yellow_off_button);
                        break;