Since version 3.5 WordPress has a new color picker, the HiDPI-ready, CSS gradient-based color picker called Iris.
Recently when I was developing custom sites for some clients I needed to use their corporate identity colors and I got tired of copy-pasting the different hex codes in the color picker all the time. So I started to look for a way to add custom colors to the color picker. At the end I succeeded. Read on to see how you can do it as well.