Frank Herbert was a mycologist. It is not widely known that the blue eyes of the Fremen in Dune are an homage to the cerulean blue of Psilocybe mushrooms.

In Chapter 9 of Mycelium Running, Paul Stamets reveals:

“Frank went on to tell me that much of the premise of Dune—the magic spice (spores) that allowed the bending of space (tripping), the giant sand worms (maggots digesting mushrooms), the eyes of the Fremen (the cerulean blue of Psilocybe mushrooms), the mysticism of the female spiritual warriors, the Bene Gesserits (influenced by the tales of Maria Sabina and the sacred mushroom cults of Mexico)—came from his perception of the fungal life cycle, and his imagination was stimulated through his experiences with the use of magic mushrooms.”

— https://www.bartkasperolaw.com/dunes-magic-mushroom-origin-s...