From Garry's Mod
Called to allow override of the default Derma skin for all panels.
|NOTE||This hook is only called on Lua start up, changing its value (or adding new hooks) after it has been already called will not have any effect.|
Example on how to use this hook. This will make that all panels
hook.Add( "ForceDermaSkin", "my_new_skin", function() return "some_skin" end )