
they can change up to about 18months of age, I have a blue & white collie who unlike his littermates had grey eyes (others had brown eyes from 8 weeks, although one does have a blue eye) I was hoping (as they matched his coat) that they would stay grey and when he reached 12 months of age, but at 16months they started to change and now at 18months they're nearly all brown... still lovely but I had hoped....
I also had a blue eyed blue merle collie whose eyes changed at about 12 months to a brown....
I believe (someone will correct me if I'm wrong) that all pups start off with blue eyes, which change colour as the eyes develop