Well the references of private purchase, multi-colour 'kerchiefs, made of various types of faberics (silk, rayon, polished cotton, etc.) I've come across, have stated that it was worn so as the Neck wouldn't chafe from the wool of the Field Blouse/Shirt, keep the neck from getting sunburnt & could be pulled up over the nose & lower portion of the face to cut the dust, blowing or otherwise.
So, it was propbably knotted in such a fashion that it could be adjusted as needed, say some sort of slip knot.