Could be. Depp's character could speak Vietnamese (not an easy language for Americans to learn), had presumably been through the language school in Monterey, California and was probably one of the more intelligent members of the platoon, so he might be better able to get on with a college drop-out like Taylor than some members of the platoon would.
"Chicken soup - with a beep straw."

Charlie and depps characters are supposed to be close mates but most of it was cut but it is in the book..

Sheen's character was not especially friendly with Depp's unless I missed something.
In jungle fighting there were probably conflicting motives to not stand out (ie. no bright colours) but have an identifying colour so your own soldiers could be distinguished during a clash.
http://img0045.popscreencdn.com/95321336_men-at-arms-143-armies-of-the-vietnam-war-2-by-lee-e-.jpg
In this illustration two NVA soldiers are wearing yellow field signs as a colour of the day. Apparently this was changed from day to day for security reasons.
My own feeling is that someone like Sheen's character wearing a red bandanna for no obviously military reason during jungle fighting is just asking to get shot.
"Chicken soup - with a beep straw."

I don't know about 1, but the NVA sometimes wore coloured cloth as field signs, worn around their necks as bandannas or wrapped around an arm. A French photographer, Catherine Leroy, snapped a picture of NVA soldiers n the Hue 1968 fighting wearing red and blue field signs.
http://www.terapeak.com/worth/life-magazine-1968-february-hue-catherine-leroy-north-vietnamese-soliders-fixer/322090815553/
https://www.google.com.au/search?q=catherine+leroy+photos+vietnam&biw=1040&bih=632&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjZ1ICRkfbNAhVdFMAKHRcJAL0QsAQIGg#imgrc=tcIopJMGwzvMWM%3A
"Chicken soup - with a beep straw."