Young Sydney has green eyes, adult Sydney has brown eyes.
There is a flashback to the day Sydney was recruited by SD-6. An admirable effort was made to match it to the season 1 credits scene showing the same thing, but among the differences: Sydney's hair is different; her brown satchel is missing; her books are different; her water bottle is missing.
In dialog and a flashback it's revealed that Sydney lived with Arvin and Emily Sloane for a time as a child. This contradicts Sydney's previous statements that she did not meet Emily until after Sydney began working at Credit Dauphine.