MCR did an interview with a GM Central Office employee years ago. That was essentially what he stated. Colors specifically excluded were Cadillac colors with heavy metallic content-"Firemist" was the term I believe.
One of the strangest special paint '69s I know of is a COPO-RS out of a dealer in Detroit. It is white but not Dover white. It is Can-Am white, a Corvette color and both are listed as '69 Chevrolet colors. Hardly looks different.
Go to autocolorlibrary.com and imagine what was possible!