title: Icon color of chrome extension changes when visited specific page
body: <p>I have encountered some chrome extensions which changes their color of icon (possibly when activated or enabled), I don't know how it works </p>
  
  <p>My question is: How can I achieve same functionality?</p>
  
  <p>I mean is it because when some specific pages are visited then they get activated or is there something else.</p>
  
  <p>I am confused, how does this work? </p>