Unity 2D has been updated to version 5.8 in Ubuntu 12.04 LTS, bringing long-awaited features, that mark an important progress point in delivering a consistent desktop with common attributes, such as the color borrowed by various desktop components,
Consequently, when changing the wallpaper, the Dash "steals" the wallpaper average color and displays a different color per wallpaper (just like in Unity 3D), furthermore the chameleonic behavior has been adopted by the launcher, the panel and the HUD, thus delivering a fancy, eyecandy shell.
Unity 2D 5.8 continues its road towards multimonitor enhancements, gaining support to display a launcher per primary screen or a launcher per screen, options available under
System Settings-->Displays-->Launcher Placement, as well as the ability to enable/disable sticky edges (when moving the mouse pointer between screens) under
System Settings-->Displays-->Sticky Edge check ON/OFF
The above multimonitor configuration options work (are valid) for both Unity and Unity 2D.