I think I can only guess at some of these,and I may not be totally right,as someone in here will have the proper answers.
I think for plotting their course they used to do what was called 'shooting the sun' ,or stars,using a sextant? (correct me),that way judging by where the sun appears on the horizon they could get an exact position of their uboat,mark it on the map,and then go from there.
The red lights are used at night,to allow their eyes to get accustomed to the dark better,its not as intense as a white light,and if they needed to rush to the top their eyes wouldnt be blinded as much by the bright lights used in the day.
Im not sure about the blue lights,obviously it was emergency lighting of some description,hmm.
The goggles may have protected their eyes from any source of light interferance,so if a ship was spotted in the dimness of night they would probably be able to see it better as their eyes would be trained for the darkness,via the goggles.Its like looking into the sun,for a moment you have a blind spot,then it goes away.That blind spot from any lighting could affect you spotting a ship in front.
Or maybe a sudden drop in pressure as the hatch is opened,and the goggles would prevent their eyes from being sucked out? (obviously a joke)
Somebody will no doubt correct me here i'm sure,but thats my guesses out of the way
