This is one of those much-debated subjects that pops up regularly
on various forums (fora ?) and can result in much gnashing of teeth
and pulling of hair.
Anyway, my understanding is that, although there would a number
of shades, most were off-white /very light cream. Not grey.
This post on TMP covers the subject well :
I did like this coment :
"...people were debating which breed of sheep would provide the wool
used in the coat." Clearly, wargamers now have wide experience in
One important factor to bear in mind is the state such a light colour
might be in after a few weeks in camp (particularly as the coats were
brushed clean, not washed).
Whatever your interpretation of 'off-white' you can be pretty sure that
at least one frenchman would have worn that colour !!