I ended up other day being on BBC page. I was browsing it on Chrome for Android and I noticed something strange.
The colour of address and header bar was red!
"Wow! That's cool", I thought. Seconds later I started to ask myself how did they do that.
Turns out it is a very simple thing.
All what you have to do is to add this meta tag:
<meta name="theme-color" content="#FF0000">
Replace the content attribute value with your colour and voila!
You can check a simple demo here: http://evilcat1337.github.io/custom-chrome-header-colour/
Github repo: https://github.com/evilcat1337/custom-chrome-header-colour/tree/master