I believe that the low interest in scope colors other than black is usually due to the fact that they come at a premium. Example, the tan S&Bs or ZCOs are hundreds of $ more than the black ones(at least here in Europe). Even if one could afford that, it's a huge $ difference, to the point that you can get a decent mount or a different color....
Black:
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FDE:
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I'm sure that more people(myself included) would choose a different color if price didn't play a role, especially when it comes to "budget" scopes. Then again, black car rims are still a thing, so I might be wrong.