The Curious Tale of Mr Spearfish - S3-E1
Character mistake: The whole mystery kicks off when Creek sees a photograph of Alice Spearfish with her parents and concludes that she is adopted because two people with blue eyes cannot have a child with brown eyes. An obsessive polymath like Creek must surely know that that is wrong. The genetics are complex and though uncommon, it is possible for a couple with brown eyes to have a child with blue eyes and the other way around. That's what recessive genes are all about.
The Curious Tale of Mr Spearfish - S3-E1
Continuity mistake: The bullet marks on Lenny keep changing places.
Suggested correction: Jonathan actually states it's a photo of 2 blue eyed parents and a brown eyed daughter.
Which is still possible! It isn't even uncommon. Brown eyed parents can have a blue eyed child and vice versa - that's what recessive genes are all about.