Mark Zuckerberg created Facebook’s original blue interface because he is red-green color-blind.
Zuckerberg has explained that blue is the color he can see most clearly. Facebook’s early website therefore used blue prominently in its interface, including the header and navigation elements.
The color choice was practical rather than a carefully engineered brand strategy at the beginning. Over time, the blue design became strongly associated with Facebook and remained central as the company expanded from a university website into a global platform.
This fact is sometimes mixed up with Facebook’s corporate branding or with the identity of the company’s other founders. Eduardo Saverin, Dustin Moskovitz and Chris Hughes helped establish Facebook, but the color-vision explanation is specifically associated with Zuckerberg.