Reading this question, I came across the below image:
If you look closely, you can see that Data's eye is blue! Now, out of universe, Brent Spiner's eyes are blue, so that's the out of universe reason why, but I'm interested in the in-universe explanation of why Data's eye was blue. I thought in First Contact the Borg were just adding real skin to Data, not actually messing with other parts of him such as his eyes.
Indeed, even Memory Alpha states that
[the Borg Queen] embarked on a transformative process to make Data more "Human," by attaching Human skin onto his android skeleton.