I would like to point out that the fabric used to cover older aircraft is not "canvas" but some form of linen or in some cases unbleached muslin (basicily the same thing that bed sheets are made out of - been more than one aircraft covered with bed sheets). The stiffness of the fabric comes from the coats of dope (either butyrate or nitrate) with which the fabric is coated (painted actually).
Basic aircraft fabrics can be found in color in colors that range from very light greys, to tans to whites depending on what materials were used in their manufacture (unbleached cottons tended to be a light tan) Up until camoflage colors were introduce, the basic cloth colors were simply covered with clear dope and then the aircraft was flown. In most cases this resulted in a gloss light tan finish. However, the Germans started printing camoflage on the fabric, applying the fabric and then applying dope over that.
During and before WW l this caused no real problems because most aircraft were recovered or destroyed in a short period. During the mid 20s it was discovered that the ultraviolet rays of the sun caused rapid deterioation of the doped fabric and it was found that by applying a coat of silver dope over the clear dope the rate of deterioration was retarded. The regulations today call for three coats of clear dope applied by brush (sanding between coats recommended) followed by three coats of silver (aluminized) dope brushed on (sanding between coats recommended). After that you can spray on any color coats that you want.
Sorry about the rant, but after 35 years of working on flying machines, this is a subject near and dear to my heart.