What about eye color?

I know this wasn't a high-effort thriller, but if I understood this Prosopagnosia right, she can't remember the faces, so it seems like a new face every time she looks at it, but the actual features of the face don't change, right?

So, if someone has a scar, she would see the scar every time she looks at him. Kinda like the neurologist explains to her with the small rocks. So, if someone has blue eyes, he would have blue eyes every time she looks at him, no?

And her boyfriend had blue eyes, but the killer had brown eyes. So when the killer tries to pass as her boyfriend to trick her, shouldn't she realize this instantly?