Whipped this half-assed sketch showing how a Zel's eye works - in this case, using Xeon as an example.

Shading was kinda... meh, so forgive the really rushed work there (and the lack of trying to make it look like he's in blacklight) but here's a basic rundown...

On the left, you have him as you'd normally see him. No noticeable pupil - just what seems to be an iris. Just color and the whites of the eyes... under blacklight, depending on the angle, typically when it hits JUST right, it's possible to get the very subtle hint of their pupils, almost to the extent how dogs and cat's eyes glow at times in dim light, reflecting whatever light is there.

Another unusual fact - a Zel's pupil is almost always dilated as much as possible, and only really shrink to a small size when trying to pick up a specific range of light or are in incredibly strong sources of light. When they DO shrink the pupils down, one might see the pupil as a small, dark colored dot in the center of the eye.