Since the LEDs are red, any tinting of the cover - even red - would reduce the intensity of the light coming through. I think the reasons for red covers are (1) insofar as the taillight acts as a reflector, it will be a red reflector, and (2) people might think a light with a clear cover wouldn't produce red light. We're used to car taillights which have to have red covers to filter the broad-spectrum light coming from the incandescent source.

Doesn't the garden-variety PBSF have a cover with a clear portion over the main LED?