See the question and my original answer on StackOverflow

Define the OpenThemeData API and DrawThemeTextEx, as well as some required structs and constants:

    [DllImport("uxtheme.dll", CharSet = CharSet.Unicode)]
    private static extern IntPtr OpenThemeData(IntPtr hwnd, string pszClassList);

    [DllImport("uxtheme.dll", CharSet = CharSet.Unicode)]
    private extern static Int32 DrawThemeTextEx(IntPtr hTheme, IntPtr hdc, int iPartId, int iStateId, string pszText, int iCharCount, uint flags, ref RECT rect, ref DTTOPTS poptions);

    private struct RECT
        public int left;
        public int top;
        public int right;
        public int bottom;

    private struct DTTOPTS
      public int dwSize;
      public int dwFlags;
      public int crText;
      public int crBorder;
      public int crShadow;
      public int iTextShadowType;
      public int ptShadowOffsetX;
      public int ptShadowOffsetY;
      public int iBorderSize;
      public int iFontPropId;
      public int iColorPropId;
      public int iStateId;
      public bool fApplyOverlay;
      public int iGlowSize;
      public IntPtr pfnDrawTextCallback;
      public IntPtr lParam;

    // taken from vsstyle.h
    private const int WP_CAPTION = 1;
    private const int CS_ACTIVE = 1;

And then, call it like this:

IntPtr handle = OpenThemeData(IntPtr.Zero, "WINDOW");
DrawThemeTextExt(handle, hdc, WS_CAPTION, CS_ACTIVE, ...)

The WS_CAPTION and CS_ACTIVE values match .NET 2's Caption and Active respectively. Values are described here officially: Parts and States