Can't provide a firm answer, but recall black anodized parts appearing in the early-mid 1970s.
FYI, there is a pair of what appears to be factory black anodized Universal "Super 68" sidepulls for sale on eBay:
Since these brakes were introduced in 1968, and continued production through the late 1970s, hard to definitively date when they were anodized.
Regards,
Kevin Kruger - Grantville, PA