.Net - Detecting the Appearance Setting (Classic or XP?)

Answer 1

There's the IsThemeActive WinAPI function.

Answer 2

Try using a combination of GetCurrentThemeName (MSDN Page) and DwmIsCompositionEnabled

I linked the first to PInvoke so you can just drop it in your code, and for the second one you can use the code provided in the MSDN comment:

[DllImport("dwmapi.dll", PreserveSig = false)]
public static extern bool DwmIsCompositionEnabled();

See what results you get out of those two functions; they should be enough to determine when you want to use a different theme!

Answer 3

Personally, I use the following to see if the app is running under themed:

if (Application.RenderWithVisualStyles)
{
    // you're themed
}