Great, first cup of coffee, and you are putting me on the spot! LOL
First that color choice was BP, (before Palmer) so please don't shoot the messenger. And for the record, I bought a Brand-New Grabber Green Maverick, and followed that up with a Brand-New Lime Green Fiat X-19, so I'm not claiming to learn anything from history.
I'm sure it's just the same in any industry, when the bridge sway's violently and falls into the Puget Sound, you will not be able to find any engineer that claimed to be the bridge designer. Colors and product names are the sole property of the Product Managment Group. As much as I joke about it, it's a really tough position to predict the future consumer demand. I think their goal is "more rights, than wrongs". In my experience the best product managers and designers are the guys the eat, breathe, actually use, and live with their products. Chip Foose is an incredible automobile designer, not only is he a "credentialed designer", but he also lives with his product. He's not a hermetically sealed in an office building, he's out always looking, and experiencing what people like and how products are used. If you look back on the Old Towne Orange vintage bike ride photos you will see him on a Sunday morning ride with HIS Vintage Schwinn Beach Cruiser. In the early 1980's companies moved away from hiring "street smart" employees with extensive resumes and if you did not have a degree in the specialty they needed, your resume was set aside. Even today almost fifty years later, I have mixed feelings. When I drive across that bridge, I WANT TO HAVE that young "just out of school engineer" with the most current design training under his belt. But when I go into the store and buy a new Renn Spooner shirt I want a designer that is living at the beach, wearing his product, and is tuned into the latest colors and styles. You do not learn all of this stuff in a university setting.
I'm going to leave it at this point. During the 1980's the head of Schwinn's Product Management group was an accredited former employee of General Mills, and his product responsibility was the Wheaties Product Management. He was a good and likeable guy, but a "numbers crunching" guy without the hands-on grass roots experience in bicycles.
The Sting Ray days were fifteen years before I landed at Schwinn. I have never seen or heard of a black Sting Ray in the line, or able to be factory ordered. It was not unusual for them to assemble a bike for product management to review. It could be a color, or different accessories for review. If you determine the Black Sting Rays were actually "factory built", I'm sure they were just a small special run. It's not that unique, they were painting with black paint, and they were building Sting Rays, it was a simple adjustment to the order sheet. It was not a major engineering and frame stress testing exercise like they did on the "Z" bike.