title: how to change the background color of Fl_Window by pressing Fl_Button
body: <p>Can anyone tell me, how to change the background color of Fl_Window by pressing Fl_Button. I'm trying to do it this way but it's not working.</p>
  
  <pre><code>void new_color(Fl_Widget* w, void*){
  Fl_Button* b = (Fl_Button*)w;
  b-&gt;parent()-&gt;color(FL_RED);
  }
  
  
  int main()
  }
  Fl_Window* win = new Fl_Window(...);
  win-&gt;color(FL_WHITE);
  win-&gt;begin();
  
  Fl_Button* but = new Fl_Button(...);
  but-&gt;callback(new_color);
  
  win-&gt;end();
  ...
  }
  </code></pre>
  
  <p>thanks!!!</p>