Question: what is the chance of a child having purple eyes and what causes their eyes to be purple?

Matt Bawn answered on 8 Mar 2018:

I remember reading (on the internet so be cautious of what I say) a few years ago that the incidence of purple eyes is around 1 in a million. Now when I try and search it seems there is alot of controversy anout whether the even exist!
In the end I found this reference: https://www.nature.com/articles/jhg2010126

which states:

“Red and violet eyes come from a lack of pigment. The red appearance is the reflection of the eye’s blood vessels. When there is too little pigment to produce a strong blue color, the red reflections interact with the small amount of blue, producing a violet color.”

Now as this was in the journal of human genetics I wouldn’t immediately dismiss it. and it does reference another paper:

which has something interesting to say about how we think about the genetics of eye colour: https://www.sciencedirect.com/science/article/pii/S0168952504001593?via%3Dihub

“Although not common, two blue-eyed parents can produce children with brown eyes. The apparently non-mendelian examples of iris colour transmission from parents to offspring, combined with the quantitative nature of iris pigmentation indicate that the inheritance of this apparently simple trait as a dichotomous value must be reconsidered. The use of eye colour as a paradigm for ‘complete’ recessive and dominant gene action should be avoided in the teaching of genetics to the layperson, which is often their first encounter with the science of human heredity.”

So maybe more research is needed.