I believe that Black cycling clothing was originally used for the then illegally organised UK TT road races around the 1890's, so you couldn't easy be seen.
"Unsure of the legal situation, riders dressed from neck to ankle in black to make themselves less conspicuous, never wore numbers but always carried a bell. Races started in the countryside at dawn on courses referred to only in code. Even the cycling press was asked not to say where a race was taking place and details to competitors were headed "private and confidential" up to the 1960s."