Demon eye colour tends to be indicative of their status and what they represent. Here's one chart that explains it.
artists painting reflections in eyes | ... Art: Photo Manipulation Artworks of the Human Eye | Design Juices
Demon Eye by acjub.deviantart.com on @deviantART
The artist(S) on my FC could have black eyes, giving an uneasy effect on the reader that makes them intrigued to know more about the content.
silentium-v-amoris: Because You see Nothing but Corrupt and Darkness within.
Cathy would love the strange and desolate eyes depicted in this picture.
Dark Witch Eye by asdfgfunky deviantart
"My father wanted her to be the future queen of hell. They were not exactly thrilled to find me in bed with a pop star three weeks later."