Ivory, as in made from elephants.

You probably need at least 9 elephants for a decent tower. Not sure how you convince them to stay still though. Probably feed them some Mnokeys.

Note: There are export restrictions on transporting elephant products across national borders.

Also the secluded environment of theoretically-oriented Universities and academic departments. Quantum physics is is performed in the IvoryTower, mechanical engineering is performed in the RealWorld and clinical medicine is performed in MeatSpace.

Also also, the 'computer case'. Although they're more off white.