I find that it happens with a few skins the one I am currently using is "Clear". I love it. The same thing has been occuring on two different systems I use. I suspect it is to make the text readable. but "Clear" is not clear.
System info is:
Your computer has a Windows Experience Index base score of 3.1
Your Windows Graphics Experience score is 3.4
WindowBlinds version : WindowBlinds 6.1 (build 91 x86 - Vista Edition)
WindowBlinds is installed correctly on this PC
WindowBlinds appears to be activated on this PC
(Generic PnP Monitor) 1 is attached to Mobile Intel(R) 945 Express Chipset Family
(Generic PnP Monitor) 2 is attached to Mobile Intel(R) 945 Express Chipset Family
Wblind.dll 2008/03/17 12:45:20
Wbsrv.dll 2008/03/18 11:54:06
Wbconfig.exe 2008/02/20 14:52:33
Wbload.exe 2008/02/14 12:05:14
Wbhelp.dll 2007/08/27 12:54:07
Tray.dll 2007/09/12 18:58:21
Wbload.dll 2007/09/12 18:58:28
Screen.exe 2008/01/11 13:14:18

This is after adjusting the color intensity.