A coating composition and a method for coating metallic substrates, such as aircraft components exposed to elevated temperatures and/or oxidative conditions. The coating composition includes an aqueous mixture having about 2 vol % to about 50 vol % organosilane, about 0.3 to about 25 vol % metal alkoxide, and about 0.1 to about 30 vol % organic complexing agent. The coating composition may be deposited on a metallic substrate and cured to form a sol-gel coating on the surface of the substrate that is adherent to the substrate, and oxidation and discoloration resistant.