Goto the folder where ur theme is stored. Most probably it'll be in following folder:
%windir%\Resources\Themes\xyz
Where "xyz" is ur theme folder.
Now under "xyz" folder u'll get following folders:
\Shell\normalcolor\
In this folder, u'll get a file "shellstyle.dll". U hv to replace this file with default Luna "shellstyle.dll" file, which will be situated in:
%windir%\Resources\Themes\Luna\Shell\NormalColor