Do you have photos of the chick when it had brown eyes?I am positive that they changed from a brownish color to this color. I've been checking on one of the chicks regularly for a slipped tendon so I noticed the change in color in the eyes.
Usually blue or green tinted eyes will turn to bay color as they mature. I've had Barred Rock that had green eyes and they eventually turned bay.
There's nothing to worry about.