I think your metaphor makes sense: there was no turning back to the paradise of the mountains. "As they descended the slope Ennis felt he was in a slow-motion, but headlong, irreversible fall " says the SS and the screenplay adds "..more emotion stirring in him than he can handle".
Though Jack did wear that shirt, at least once, before while Aguirre was visiting the mountains about Jack's uncle.




Or am I 'colourblind' here? 

No,rdx,you're not "colourblind" here and me neither.I only said that according to what I remembered,Jack was wearing a new shirt,but it's clear enough that I remembered bad.So,it's a matter of bad memory,not of bad view ¡.
I'm with rdx here. It was a "new" shirt on Ennis and definitely can point out the new life he was about to enter.(That's a great parallel, MPJ!!!) But Jack had the same shirt as before. He obviously wants to continue with the same life style... 
This scene is so sad... so very sad. When the most beautiful time in someone's life is over!!!


I agree completely with the shade you add to the subject here,Loreen ¡.And

for your words too ¡.Yes,Ennis wears a new shirt but not Jack...It can be the translation into clothings and images of what we see in the lasso's scene,when Jack is happier than Ennis because he believes they are going to see each other down the mountain,while the second one knows for sure this isn't going to happen...Jack wants to continue with the same life style,so the same shirt.Ennis won't continue it,so he changes his clothings,that,moreover,has a darker brown than his shirt up to that moment...Maybe this means that he comes back to be with his feet on the ground?Since brown colours mean Earth and the attachment to this Ennis has,while Jack has blue,that means the air...
