Not really. AA left their planes unpainted for decades and they were fine because aluminum is naturally corrosion resistant through the formation of aluminum ox

Not really. AA left their planes unpainted for decades and they were fine because aluminum is naturally corrosion resistant through the formation of aluminum oxide. However, the aluminum dulls and needs to be polished regularly to not look like shit. Also, the composite surfaces need to be painted to avoid UV damage, so most airlines just paint everything anyway.