Luke has no name writes: "The "human" OS is getting some makeup. For the upcoming 10.04 LTS release, Ubuntu's theme is getting revamped. Its logos, default themes and panel icons are all changing to reflect their new "Light" theme.
The new style of Ubuntu is driven by the theme "Light". We've developed a comprehensive set of visual guidelines and treatments that reflect that style, and are updating key assets like the logo accordingly. The new theme takes effect in 10.04 LTS and will define our look and feel for several years. — Source"