I'm interested in what others have to say on this...but here are my thoughts.
Pullets do develop different eye color from chickhood, so that is a possiblity. her adult color coming in. (I have had Marans which naturally have a copper eye).
However, looking at the left eye, I am also seeing some irregularity in the pupil. Is that from camera angle? Or is that the way the eye looks?
If so, my best guess is Ocular Marek's which changes the color of the iris from the tumor growth as well as the shape.
There isn't anything you can do. It can progress very slowly. The other birds have been exposed already, but if Marek's, you can decide if you want to cull this bird.
I'm not thinking it is any kind of eye irritation as the eye itself would be bloodshot and swollen, and while the membranes are a bit pink, I don't think they look infected.
Marek's often strikes just before point of lay, which this young pullet looks to be about at.
Hopefully someone has a better thought than I do.
LofMc