Very interesting, Barb! I've been wondering about the placement of that hat on the wall, too. A halo? Jack's spirit hovering? Gotta be somethin'.
I like the idea of the symbolic trinity, too, and that's a great little bookend when you compare it with the three telephone poles at the beginning. Of course there is a real crucifix on the wall by the kitchen, too.
I posted somewhere awhile back about the use of red after the Scene at the Lake. Casey Cornelius once wrote that all the scenes after that had a kind of hallucinatory quality, and there does seem to be a subtle but real draining of color out of the movie towards the end. But dropped into the midst of these drab scenes are touches of red.
Ennis wears the same grey overshirt in the last four scenes, grey being the muted form of Jack's signature blue and also suggestive of Ennis's depressed frame of mind. The shirt has an interesting red detail right over the heart like a symbolic wound. In the same way, each of the four last scenes has a neutral palette punctuated by bits of red.
Here's a painting by Hammershoi that one of the IMDb posters postulated was an inspiration for the Twist ranch scene:
At theTwist ranch, in addition to those things you mentioned, Jack's father has a red belt, Jack's mother's dress has a small red detail in its print and her hair has a reddish tint. There are patches of red on Jack's bedspread and clothing, and finally, dark red on the bloodstained shirts.
The dreamlike quality of the scene is heightened subtly, I think, by the red dropped into the otherwise neutral tones. It does remind me of how we recall incidents in our lives--a kind of general impression punctuated by more vivid moments. If Ang Lee was trying to give us the feeling of being inside Ennis's memory, this may have been one of the ways he chose to do it.