There seems to be a trend in websites that color the address bar of Chrome on Android. While I'm not convinced this is always a good idea, it got me curious on how it was implemented.
Turn's out it's really, really easy to customize.
<!-- Chrome, Firefox OS and Opera --> <meta name="theme-color" content="#02baf2"/>
The Google Developers page on coloring browser elements covers some basics for Windows and iPhones as well.