I have always wondered if the green paint that's seemingly found on the inside surfaces of aircraft serves a special purpose and why is it always green? Lou

Lou,

If it's the light green stuff you're referring to, that's zinc-chromate which is an anti-corosion primer/coating used on aluminum. It's on the outside too just covered by the final color coat.

Not as widely used as once due to better primers available plus zinc chromate is highly toxic. A strange stuff, really.
"Zinc chromate is simply a corrosion resistant pigment that is added to certain coatings. In the case of a wash primer, the phosphoric acid actually reacts with the metal, whereas in the case of zinc chromate this is not the case. In dry, low humidity weather the zinc chromate does not do anything other than remain in the coating. On the other hand, when the humidity in the air increases, or on a rainy day moisture for the air penetrates the primer coating and slightly dissolves the zinc chromate. The dissolved zinc chromate solution now does react with the underlying metal surface and forms a passive layer (like a blanket|) that prevents corrosion. As soon as the weather becomes dry again the zinc chromate no longer pays a role ... at least until the next time it rains, when the process is repeated. If there are frequent cycles of high and low humidly the zinc chromate will eventually be depleted and soon after you might start to see corrosion of the metal.. "
[from http://www.paintcenter.org]
Mostly epoxy, polyurethane, alkyd and other primers that do not contain zinc chromate, but instead contain other corrosion inhibiting pigments are widely used today. These are more desireable as they do not leach out and are non-toxic.

Thanks! I figured it had something to do with corrosion protection. It seems that the industry has been using it for decades.

Lou