Yeah me too - according to Spencer Klein the 1976-1978 6306 & 6309 came with tan lume in varying degrees from the factory, the theory being Seiko were experimenting with different lume formulas during that time with some coming out with a heavy tan, some medium and some light. He seems to think it's linked to the production of the Grandfather Tuna 6159. Most of the '79 turtles I've seen have a more ivory white lume and that's what they continued with up until the end of production as far as I know.