I came across this cool registry setting a while ago and had to look it up again.
Open up regedit, (Start > Run > regedit) this is the main key you’re lookin’ for:
(The above alone worked for me, but some references say you also need the change the corresponding keys in HKEY_LOCAL_MACHINE and HKEY_USERS – so change them too if you’re having troubles.)
For each of these set the “DllName” key to the path to your preferred .msstyles Visual Styles file. If you want to choose a color variation other than the default for that syle, you also need to change the key “ColorName” to match the name of the folder for that variation found under the shell folder.
So with the default Luna style in Green, change “ColorName” from “NormalColor” (Blue) to “Homestead” and for the Silver color change it to “Metallic“.