It was mostly just a fashion trend that started in the early 80s and continued another 10-15 years or so.
Originally there were the exotic and unobtainable Mavic SSC rims that some pro teams used but we only saw in pictures. These were in use as early as 1978. There was also the Martano black. The Mavic SSC's and the Martanos were very expensive and IIRC heat treated. The anodization marked them as such. (actually not sure if the Martano blacks were HT, perhaps someone recalls)
By the early 80s some 'black' anodized rims showing up on obtainable bikes. These were usually just regular rims that were anodized instead of polished, and were not functionally any different. They were perceived as trick, becaused they looked like SSC's. By the mid 80s seemingly most rims had to be black, otherwise they weren't cool.
Last edited by Salamandrine; 12-06-16 at 10:14 AM.