In the Dune series, people who are addicted to melange have entirely blue eyes. Is there a significant reason as to why Frank Herbert chose the colour blue over other eye colours?
In parts of the novel, the melange users hide their colour behind contact lenses the way a real-world drug user may hide his red eyes behind sunglasses. But among the Fremen, it is referred to as a symbol of the tribal bond of the Fremen, or their "ethnicity" if you like. Again, in the real world, the gene for blue eyes is recessive and rare and blue eyes tend to be a marker for a certain ethnicity. It is simply easier to get the reader clued-in to blue eyes as an ethnicity marker when it's already recognized as such in the real world.
Alternatively, you can consider Frank Herbert's choices. If the whites of their eyes had been coloured yellow, it would sound like they had liver disease. Brown just sounds like a dog's eye, while "green" were taken by other fictional aliens.
Melange (pictured above) is by the way consumed in great quantities in Norway, where a disproportionally large number of people also have blue eyes.
What did you say about dog eyes?.. icecold stare
Got his inspiration from Nordic people? Dare to say that to my face?
Herbert's Fremen were greatly inspired by the Taureg, whose traditional indigo male turban ("tagelmust") and veil (the "alasho", worn by both men and women) often stains their skin blue. These nomadic pasturalists live in the Saharan region of northern Africa, where they continue to suffer from colonial injustices. I have seen photographs of blue-eyed Taureg (not an uncommon feature) that evoke the Fremen image perfectly.