android Asynctask thread.sleep?

In my app when user writes wrong character,my edittext becomes red then it becomes write.Actually ı am trying to make a red blink.This is my working code

 class BlinkTask extends AsyncTask<EditText, Boolean, Boolean>
{

    @Override
    protected Boolean doInBackground(EditText... params) {

        EditText et1=params[0];

        try {
            et1.setBackgroundColor(Color.RED);
            Thread.sleep(1000);

        } catch (InterruptedException e) {
            e.printStackTrace();
        }

       try {
           et1.setBackgroundColor(Color.WHITE);
       }
       catch (Exception e)
       {
           e.printStackTrace();
       }

        return true;
    }
}

but when I take et1.setBackgroundColor(Color.WHITE); out of try-catch block.It gives no error but unfortunately myapp has stopped.I checked loggat but saw nothing.this is false code class BlinkTask extends AsyncTask {

    @Override
    protected Boolean doInBackground(EditText... params) {

        EditText et1=params[0];

        try {
            et1.setBackgroundColor(Color.RED);
            Thread.sleep(1000);

        } catch (InterruptedException e) {
            e.printStackTrace();
        }


           et1.setBackgroundColor(Color.WHITE);



        return true;
    }
}

I don't know why it needs try-catch although it gives no error.

also ı want to ask creating a asynctask class for this task is a good solution or nwhat else can be done.thank you