This guy has a few colour photos from the same time period, but the Cents appear to be plain green in the 60s and green/black in the 70s.
Harold A. Skaarup, author of Shelldrake
The Cents in the photo above seem to have a high-contrast two tone scheme, perhaps sand and green or something. I suppose that they could be green/black, and the contrast is just an effect of the light and/or semigloss paint finish.