The old "Painting Aluminum Looking Aircraft Panels in Photoshop" has been added to the
Papermodelers.com Self Help Library section:
PaperModelers.com - Downloads - Aluminium painting tutorial
The file will be available as soon as it is cleared by admin.
The tutorial deals with fuselage painting and unfortunately ends at the "Wings and stabilizer" section. However, what's there is very valuable, and I guess the logical continuation would be sky colours for the topside of wings, and ground/tarmac colours for the undersides.
Leif