This new admin theme is called NiceAdmin, created by Douglas Karr of The Marketing Technology Blog.
I got tired of the drab User Interface in WordPress Admin and decided to write this plugin. NiceAdmin was built from the SpotMilk Theme, the Milk theme by Max Rudberg, and its overall main layout remains based on the default admin theme that comes with WP 2.1. I utilized the graphics and colors from the WordPress website. The CSS was fine-tuned by Sean of Geek With Laptop.
Compared to the WP Tiger Admin and Spotmilk, the NiceAdmin theme doesn’t really change anything except the colors of WordPress dashboard which is adapted from the WordPress site. However, if you prefer the original look of the WordPress dashboard and just want to change it’s colors, then NiceAdmin is for you. For me it doesn’t really have any difference with the default WordPress UI. Overall, I give it a 3 out of 5.
Check out the NiceAdmin admin theme for WordPress.