I just noticed this... The colors of the men's garments complement the green and brown colors of the structure... This is another reason why I really love this image...
A further reason this image works for me is that the vertical and horizontal lines of the structure are straight and do not keystone.
I made a subtle change by adjusting the CS6 burn tool to 50% opacity and painting over the men, This slight modification seems to help these two men stand out from the background.
You should really print this image and enter the print in a photography contest or two...