Manfred...
I remember when "black cameras" and "black lenses" came into fancy. During the Vietnam conflict, many photojournalists carried two to four cameras on straps hanging all over their body. In the early days of that war, the cameras were generally of a silver or aluminum color and many of the photojournalists would cover their cameras with dark tape (olive drab military ordnance tape was frequently used as well as black gaffer's tape when available) and some photojournalists even painted their cameras black or olive drab so that the flash of sunlight off the aluminum body would not attract snipers. At least that was the general consensus.
The camera companies began to produce black cameras and black lenses for the photojournalists and then it became a fad, If you had a "black camera" you were obviously a professional
I also believe that the Canon White came into popularity when shooting engineering documentation of weapons and aircraft. Most of that documentation was done in desert areas with long focal length lenses and the cameras/lenses were often set up in the hot sun for hours. The white color of the lens did provide some protection against the heat.
However, for uses such as sports, the white lenses were an advertising feature. When you saw an enormous number of photographers with most of them using big white lenses, it was free advertising for Canon...
However, we are now seeing a mixture of white and black lenses at sports events...