We're talking about the 1840's here.
Try an internet image search for "covered wagons", "covered wagon covers", and...while yer at it..."ship sails".
also...
Fur Trade tents
Canvas teepees
The majority of examples I found have been some shade of WHITE/off-white/light tan.
BTW...are you aware that, when left outside, fabric will fade/bleach out from exposure to the SUN??
Did y'all know that using WHITE canvas on covered wagons in a parade celebrating the Oregon Trail migration is RASIZT!!
The organizer of the event has ordered that the covers be "colored" (i.e. anything other than WHITE).
Since there is no "SHB definition" for the named sweep, the reply I posted on the linked 2013 thread still stands.
Y'all can beat this horse into a bloody mess forever as far as I'm concerned.