the human eye is less sensible to red light than o any other color, if they used white lights when the kaleun rised the scope he would see blackness (close your room so no light can get in, turn on the light, wait a few minutes and turn the light off, you wont see squat). So, by using red lights the crews minimised the efect of the lights.
if you go to the bridge of a ship, you will see that there is no light on, exept from the navigator, who has a red bulb pointing towards the maps, and there is a curtain (or a wall) so that the rest of the crew in the bridge does not see the light.
the red lights were used both at night and during attacs (or at least that's what Das Boot* shows)
it cant be controled, but it could be moded, (imagine... a button on the atack periscope to turn the lights red, just like in Das Boot
)
*Das Boot: a movie you should see!