That "DwmSetColorizationParameters" was an undocumented function which was never intended for public use. Things like this regularly stop to be supported without public notice.
For me, it works changing the "AccentColor" key in HKEY_CURRENT_USER\Software\Microsoft\Windows\DWM and broadcasting a WM_DWMCOLORIZATIONCOLORCHANGED message afterwards
Source:
http://www.pinvoke.net/default.aspx/...tionParameters
Nevertheless, I would hate an application for changing my personal settings. I'm sure you know this and have a good reason for messing the the users personalization settings
