NWGratefulDiver:Actually, it's because back in those days mask skirts were made out of rubber instead of silicone ... and rubber doesn't come in clear ...
... Bob (Grateful Diver)
And the only reason black dominated over all of those other colors is the same reason that tires were black - the molecules in rubber exposed to sunlight were broken down by UV exposure and the rubber became brittle and cracked. Carbon black protected the rubber against UV radiation, and also made it black. A red or yellow rubber mask dried up and fell apart in a fraction of the time that a black mask would survive. Somehow, a strictly utilitarian black became fashionable.