Here's a picture Joe Lucia from the NCRS sent me a few months back. (If you don't know that name, like our JohnZ (John Hinckley), he's VERY respected in the Corvette community)
It's a 1968 NOS pump dated 2568 (256th day of 1968, or September 12). Note how smooth the aluminum housing is, the extrusion marks and the color of the fan. It's not "WHITE white", but it's not "yellow" either. More of an off white or maybe an egg shell white like Kurt stated above. After time, the age of the plastic and the extreme under hood temperatures make them yellow, but that's not how they started out. Also note that original fans are two piece like Joe shows in his picture above. Repops are one piece.
By the way, Joe (Lucia) has a TON of NOS C1, C2 and C3 Corvette parts, but unfortunately, none are for sale. If they were, he'd be a bizillionaire!
Ed