title: Contrasting layer in JavaScript / HTML
body: <p>Base of my web application is a map, consisting of a lot of pale tiles. 
  So result of printing this page using B/W printer is very grievous.</p>
  
  <p>Is there any possibility to lay on some layer on the map, which will make it more contrasting?</p>
  
  <p>(Replacing tiles in print mode is a bad idea, yep).</p>