In WordPress 3.8 eight different color schemes were introduced to the admin panel. Follow the instructions below to change from one color scheme to another.
To begin, login to your WordPress admin panel and go to Users -> All Users.
On this page, locate your user or the one you want to change the color scheme for and click on the Edit link that will appear when you hover on the username.
On the top of that page you will see a list of eight different color schemes. Click on the radio button next to each one of them and your admin backend will refresh in the new set of colors.
That's it, you don't even need to press the Save button at the bottom of the page because your settings automatically update when you select a different scheme!