After looking in the 1966 Model Introduction Training Book, the 1966 Sales Brochure, the 1966 Buyer's Digest, the 1966 Color and Upholstery Book, the 1966 Only Master Parts Catalog, the 1960-68 MPC and the 1966 Ford Color Chart, the only reference I have found that addresses the colors of the GT Stripes is in the 1966 Ford Car Facts Book,printed in August of 1965 (copy attached).
However, as Jeff noted, while these may have been suggested combinations, back then, it was basically a "Buyers' Market", and just about anything that was available could have been ordered.
Bob