In the movie's kiss scene, it is definitely daytime with an overcast sky.
But, in the book, it is a stormy late afternoon, thunder growling, and it is somewhat dark at the top of the stairs up to the apartment over the laundry when the guys kiss on the landing up there. The book mentions that when Alma opens the door the 2nd time, the guys are standing side-by-side with the backs of their hands touching, in the narrow light, which implies that she did not fully open the door all the way. The light comes from inside the apartment.
Because of the description of the scene in the book, I still stand by my opinion that Alma did not see them actually kissing and only hugging with Ennis's straining shoulders blocking most of the view since his back was very close to the door. It's one thing to see "fishin' buddies" hugging when they have not seen each other in 4 years; but, if they had been seen kissing by Alma or anyone else, that would have been a different matter.
In the movie, the view of the stairway steps up to the other apartment was actually blocked from view from the street. They could have filmed the scene with the guys up on the walkway in front of the apartment door as described in the book.
Slightly OT here, some of the movie's dialog which takes place in the mountains on the 2nd night of the Reunion is actually in the Motel Siesta on the first night.