Statue of Maintenance Oxidation
the Statue of Liberty is green because it's clad in copper sheets that oxidized over time. I think it'd be neat if the Statue of Maintenance started out as bright shiny copper when first built and then it slowly oxidized and turned that dull green color over the next hundred years or so afterwards. Perhaps there could be a restoration option to keep it non-oxidized if the player wishes, in exchange for consuming extra resources/unity/maintenance