Chome on Android has a feature where you can change the colour of the address bar when users are viewing your site; all this takes is one line of HTML:

<meta name="theme-color" content="#f92672">

And now your address bar is a lovely colour!

Chrome on Android with a coloured address bar

Update: this is now supported in a lot of browsers, most notably those for mobile phones like iOS Safari and Firefox. You can also add higher-res favicon links which will be shown:

<link rel="icon" sizes="192x192" href="nice-highres.png">