That's awesome! I love these transparent prototypes. I have a transparent prototype of a force feedback steering wheel game controller from a previous employer, it's not nearly as cool as a transparent vintage Mac but maybe some day I can sell it for a fortune and retire. Yeah not likely

The transparent plastic is not likely to yellow nearly as readily as the beige production stuff, but all plastic is degraded by UV light to some degree. The high energy UV photons literally blast apart molecules in the polymer chains, causing the plastic to get brittle and crusty. With a rare and valuable collectible like this, it is certainly advisable to keep it out of direct sunlight. Even ordinary fluorescent lights emit enough UV that fading and degradation can be an issue over a long enough period of time.