God I love details, especially when it’s a character’s eyes.
You’ve got Hal with his deep brown eyes: warm and dark and solid. They’re reliable standard eyes, something familiar for the viewer in a sea of alien.
Kilowog’s red: different but subtly, warm. His eyes are can be threatening and not depending on how they’re framed by his face, like how Kilowog is with his moods.
Aya’s blue: sleek and bright, not quite naive but young. Also a tad too bright to be natural, a soft reminder that she is also alien in a different, slightly more artificial sense.
Razer is blue as well: a soft contrast to counteract the rest of his design. It hints to a kinder side when we can’t see one, just as their mild dullness in comparison to the others shows the weight, the filter, he views things through.