Thanks for the kind comments everyone. VC next, does anyone know if the scarves they wore were also in recognition colours or just random individual taste. I've seen the red and blue recognition strips on the sleeves.
A variety existed, most frequently versions of the traditional checked khăn rằn scarf, which comes in a variety of colours: black and white, blue and white, red and white and even green and white. That said there are also photos of scarves/sweat rags in solid colours and apparently the camo pattern US parachute was a popular source of donor material (you also see this used for capes).
I've read that the way the scarf was knotted and worn was used as a field sign to determine friendlies over foes. The guides at Cu Chi said the same thing so maybe it's true but probably irrelevant to 28mm minis either way.
Possibly for particular ops scarves may have been worn in particular colours, just as recognition flashes were used from time to time. In addition to the patches used at Hue If you look at footage of the liberation of Saigon, there are troops shown wearing solid red armbands. On the other side of the equation Australian troops occasionally wore field recognition signs in their bush hats, most frequently the pull-through flannelette threaded through the loops in the hat.
I've tended to go with a mix of solid and black/blue and white checks for mine. I converted some Khmer Rouge a few years ago and went red/white with their near identical kramas.