In the late 1970's I used a lot of slide film. The one I liked the best for its natural colours (to me anyway) was Perutz Peruchrome C19. The speed was equivalent to ISO 64. It was made by Agfa, possibly in the Perutz plant (it had their Munich address on the boxes). It used the Agfa slide process, not E6, and the slides were mounted in green plastic mounts. I think from memory it was eventually replaced by an E6 film (Peruchrome 100?) but by then I mainly used print film.