Nothing on an order sheet or broadcast sheet to indicate scoop color.
No definative cut-off dates exist that I know off.
I've posted this before but here is the part of the Fram blueprint with their respective Chrysler part numbers...three colors only, red, silver, black were what Fram assembled and shipped off to Hamtramk for production line cars.
Plenty other colored scoops have been seen on cars in ads ( purple scooped Challenger convert ) and magazine test cars ( yellow scooped Cuda) but they were done for those purposes somewhere other than by the original vendor.
The only exception I was told by a Fram employee, is that he hand painted at least two orange scoops in 69 which he badged with Challenger engine callout nameplates.
Suits from Detroit waited while he painted them and left with fully assembled units claiming they were for special cars ( I'm guessing for the orange brochure shaker Challenger and press release photos).
Additionally lots of dealers would paint a scoop to match the body on a brand new shaker Cuda or Challenger sitting on their lot to suit a prospective buyer who didn't like the argent or black thus resulting in people claiming that is the way it came from the factory..