Take the hints and search for them. Area 1 - (obviously) Definition of door, Area 2 - from synopsis of the movie 'Stage Door', Area 3 - from Machiavelli's The Prince (Chap. 3), Area 4 - from movie site about Matrix #2, Area 5 - famous William Blake quote from his book Marriage of Heaven and Hell
For 15 - Blue on the ceiling, yellow right below. While endless falling, blue next to the window, then when you shoot up make yellow on the lower ledge next to the zapper.
 "The Impossible Psycho Doors"){kind=icon}
 "Portal: The Flash Version"){kind=icon}