from The New York Times -
Stripping Away the Darkness as Murals Are Reborn
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As inevitable aging of the varnish sets in, the building decor was adjusted to match the darkening shade:

"[O]ver the years the surfaces grew darker. And as the murals’ topcoat of varnish deepened, the maintenance staff painted the undecorated parts of the walls a darker color to match. After the north corridor lobby murals were cleaned, [...] the color scheme for the whole interior was out of whack."

Now, the cycle starts again - and conservation treatment somewhat plays a "renewal" role rather than one of mere preservation.
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