How very odd.

I think that the eye lid is more of a lens cap.

A shutter on a camera not only controls the total amount of light reaching the detectors but also, because it is open for a finite period of time, causes the input to each detector to be integrated over that period of time. The eye integrates the input signals over a period of time because of its response time which is in the order of 0.05 seconds. The response time does vary with colour and with brightness.