What were the colored overhead lights on German U-boats for?

Question

In the movie Das Boot, when the sub is attacked with depth charges the overhead lights change from red to blue and back and then back to white. What is the purpose of the colored lights?

Answer 1

These adjusted your night vision. If you were running below the surface and were getting ready to recharge on the surface at night the red lights saved your eye sight so you could see alittle better in the dark.
Same prinicipal as you walk outside your house at night and you can't quite see in the dark until your eyes adjust.
Oh...good movie by the way.