Greg, I agree that, upon first glance, Lime Gold is not rare--after all, it was Ford's most popular color for 1967 and may have been up there for 1969.
But if you glance at the Marti, it shows to be about 6-700 for the fastback, which is about 7% of fastback production. I'd guess that's middle of the road for colors for that car.
FWIW, I don't think the bench/auto combo is remarkable. Don't forget, the Cobra was the response to the Plymouth Road Runner, so many cars came with bench.