Human eyes, or rather irises, under normal circumstances have three base colors—brown, blue, and green—and based on the variations of these three, there are a full nine eye colors in total, a dazzling variety.
Yet among these nine, there has never been "crimson red"; there is only pink, and even that is caused by albinism later in life, not the natural color of human eyes.
Through certain technological means and gene-editing techniques, humans can of course manually turn their irises red, but that red is quite different from pure crimson, and it's the kind of difference any ordinary person can spot at a glance as wrong.
So in theory, in this world, it is impossible for someone to be born with naturally crimson irises.
