It's possible that when nobody is working in the room, the lights aid in maintaining a sterile environment.

At specific wavelengths (~245-265 nm), (UV) light inactivates quite a few living things. As light is quantized, the purpleish color you see is due to e- stepping down.

Clean rooms that work with semiconductors use light-sensitive photoresists. I've always dealt with yellow windows and yellow covers over the lights, though in theory pink would accomplish the same thing: keeping blue light off the wafers while you're working with them.

The concept is not at all dissimilar to old-fashioned darkrooms in photography. Outside light will wash out your image.

Certain parts of the cleanroom will look yellow--these are the spaces where they do lithography with resists that are openly accessible to the air. UV-sensitive resists will chemically crosslink in UV light, so they put on filters on the fluorescent lights (or use special lights) that keeps the wavelength away from the higher-energy blues and towards the lower-energy yellows and reds.