A Windows visual style allows to define the general appearance of windows, menus and the taskbar.
Example: on the left, the default Windows 7 visual style. On the right, another visual style where windows transparency have been changed.
Windows visual styles can have transparent window borders since the arrival of Windows Vista. Nevertheless, a « basic » mode without transparency is always present on computers which don't support « Aero » mode.
Images and color codes which define a visual style are contained in a « .msstyle » file.
A visual style must be created for a specific operating system. For example, a visual style designed for Windows Vista won't be able to run on Windows XP and Windows 7.
Likewise, a visual style must be signed by Microsoft to run. Indeed, Microsoft put protections which prevent us to apply an unsigned « .msstyle ». However, this restriction can be easily unlocked by changing the « uxtheme.dll » file. And CustoPack Tools automatically changes « uxtheme.dll » !