Plex

Plex was the main visual style for earlier builds of Windows Longhorn. It was featured as the default theme from builds 3663 to 4039. When it first came out on build 3663, it was simply an altered Silver Luna theme. However, it was changed to feature an almost all-blue user interface with a prototype sidebar. The theme was removed for build 4042 and replaced with Slate: the development team never intended for Plex to become a finalised theme[source?].