As I noted in my feature post on WordPress 3.8, the new WordPress build tools (using Grunt) and the port of the admin CSS to Sass make it much easier for WordPress core to make new admin themes. Well, with Admin Color Schemes, the heart of the admin theme compiler in WordPress core is duplicated, offering an excellent sandbox for anyone that wants to create their own admin themes.
If you are familiar with Grunt (this will help if not), then the setup for making admin themes will be fairly straightforward to you. The meat of each theme in Admin Color Schemes is only about 5 lines of code, where four baseline color variables are reset.
So, people that really want to customize their admins for clients or SaaS projects can do so more easily with this setup. Or you could just install this plugin if you want to use one of the included 8 additional themes, and I’m sure more will come down the line.