Originally Posted By: Dr.House
My guess is the exposure of UV rays from direct sunlight over time turned the white cabinet yellow.

This indeed looks like sun exposure (note the still white outline as light would have been blocked by the grille plastic).

UV energy is very high intensity. Short of a metal surface (and even that is susceptible in a different way), every material will exhibit some type of change being exposed to UV light on a daily basis.
Such is the function of energy.

"Those who preach the myths of audio are ignorant of truth."