The theme engine in Windows XP was a major update to the OS, allowing for third-party themes and lots of customizability. Microsoft famously moved to a blue and green Luna theme for the final version of XP, which many dubbed Fisher Price-esque when the OS was originally released in 2001. The theme itself is described as a “Whistler skin with eye candy,” and marked as “for internal use only.” Whistler was the codename for Windows XP. Windows developers appear to have used the theme as a placeholder to build the theme engine for Windows XP. Microsoft never released its Aqua theme for Windows XP, and we understand it was used in early source code for the OS. Although the theme is incomplete, the Windows XP Start button and various buttons and UI elements are clearly themed to match Apple’s Aqua. One is labeled “Candy” and includes a design that closely resembles Apple’s Aqua interface that was first introduced at the Macworld Conference & Expo in 2000.
A recent Windows XP source code leak has revealed Microsoft’s early work on the operating system and some unreleased themes the company created during its early XP development back in 2000. Microsoft created a secret Windows XP theme that made the operating system look more like a Mac.