Could this be a form of PPA?

I recently had my youngest a month ago, I instantly noticed his eyes were a different color. Both parents have brown eyes & my oldest 2 also have brown eyes. My newest addition has hazel grey eyes. Since we’ve been home I’ve taken him to the doctor 3 times ensuring his eyes are okay & his pediatrician says they are his eyes are just different but I personally can not accept that. I spend endless hours on google researching what could make his eyes this color, I did reach they could possibly change in color and I hope they do my anxiety has been through the roof, & my fiancé has tried to understand from my stand point but he just says also his eyes are different…I keep asking why & nobody can answer me.