Eye colour

[Fireants]

Mum 1, Dad 1 and son 1 have brown eyes. Son 2 at 6 months has piercing blue eyes.

Mum’s mum has blue eyes and all her siblings and parents have blue eyes.

Please explain why Son 2 has blue eyes to calm Dad 1 down.

Both me and DH have dark brown eyes.DS has blue/green eyes and DD has blue eyes.