There are no hard "rules" regarding the these linen colours, only likely "best guesses" at the various appearances of different grades of linen available at the time.
Any manufacturer's colour callouts have to be considered speculative. Ours are based on knowledge of flax and linen types available 100 years ago and study of surviving samples. As an antique dealer and restorer for twenty five years - specialising in antique paint finishes - I have applied my "eye" and experience to this project.
The modeller must gauge which he likes the look of - the titles are merely a guide.
Early linen used by all sides was of the pure Irish and Belgian quality and very pale in appearance. Discoloured by dope and varnish then in the field deterioration and staining for their short service lives, numerous effects can be considered and achieved and the "linen effect" decals help reach a new level of experimentation.
As supply lines were broken German aircraft manufacturers had to use whatever they could get hold of and quality became erratic - even linen intended for tableware was requisitioned and printed on, sometimes overprinting recalled stocks! An unbleached appearance was noted as common and replicated. French linen samples I studied appeared different yet again - a yellow tinted effect perhaps caused by tinted dope coverings rather than its natural state.. But these observations can in no way be declared "fact" - but interpretations I am happy to stand by as a modeller and amateur historian.
As with the PC10 argument, light, age, the time of day and weathering can have a huge effect on the appearance of any dye or paint appearance so arguments declaring one colour or the other as "correct" can never be conclusive. What I do is produce the best interpretations of my studies that I can and always try and base these on examination of actual samples.
Best wishes, Richard