Yes they are not painted, plain ugly dull magnesium gray. My point is about galvanic corrosion, at the dissimilar metal connections such as the valve cover bolts on the cover.
"Coating the magnesium for protection against galvanic corrosion is not recommended. The reason is that coating defects are easily introduced during assembly and also during service. This defect in the coating on magnesium creates a small anodic area compared to the large cathodic area. When the coating is essential with for example automotive parts like inner door frames, robust coating systems are necessary so as to withstand the assembly forces as well as the dynamic forces during service."
http://www.magnesiumsquare.com/index...d=27&Itemid=42