Several themes were developed by Microsoft but were either leaked or used only during development.
The Ultimate Guide to All Windows XP Themes: Nostalgia, Customization, and How to Get Them Back
Also used Olive Green, focused on Renaissance sketches.
Windows XP transformed the personal computing landscape not just with its NT-based stability, but through its radical departure from the "grey" aesthetic of previous Windows versions. Central to this transformation was its new theming engine, which introduced "visual styles" that used bitmaps and rounded edges to create a softer, more modern interface. The Core Official Themes
Software suites (like the Longhorn Transformation Pack or Mac OS X Transformation Pack) modified system files, icons, and fonts to completely mimic upcoming or competitor operating systems. Legacy and Modern Preservation
Released to promote Microsoft’s portable media player, this theme introduced a bold black and orange color scheme that felt "edgy" and modern compared to the primary colors of Luna.
Before Windows Vista launched, thousands of XP themes emulated its dark, translucent "Aero" look.
Originally for Media Center Edition, this is widely considered the "cleanest" official XP theme, featuring a vibrant, glass-like blue.