You're probably right. (Or wright, as the case may be. Sorry; it's a hot and humid night here in the Southeast.) This particular subject has more in common with sailing ships than with any other kind of aircraft.
I took a look at the real thing just a few weeks ago, at the Smithsonian. It's been restored (for the umpteenth time) fairly recently, and now resides in an extremely interesting gallery that's devoted entirely to the Wrights. The old artifact obviously has aged quite a bit. The canvas has been replaced several times, and I'm fairly certain most of the wood parts have been refinished at least once. So take all the following with a large grain of salt.
The canvas currently on the aircraft represents the best efforts of the Smithsonian curators (who are just about the best in the profession) to replicate the original. It's bare, apparently untreated muslin, or something similar - an off-white in color. The color in which the Revell/Monogram "canvas" parts are molded is in fact quite close to the original. It does have the unmistakable look and sheen of unpainted plastic, though. If I were building the model (it's on my "to-do-someday" list), I'd be inclined to paint those pieces with flat paint of just about the same hue as the plastic.
The struts and othe wood parts are, if I remember correctly, spruce. In its fresh, unfinished form it's a light, yellowish brown, but it darkens considerably with age and the application of any kind of finish. The struts on the Wright Flyer have had some kind of finish applied to them; I suspect it's shellac. (I'm sure the Smithsonian has published a detailed description that would remove all doubt.) Shellac gives a warm, slightly orange-ish cast to the wood, along with a semi-gloss sheen. The 1903 photos of the aircraft make it clear that the struts were darker than the canvas, but not nearly as dark as the brown plastic of the kit parts.
A trick I've seen applied pretty effectively to some models in the magazines is to paint the struts light brown, then give them a thin coat of Tamiya transparent orange. I haven't tried that myself, but I like the look it seems to create.
One key element of the aircraft's appearance is difficult, if not impossible, to reproduce on a model like this: the wings, "rudders," and "elevators" were translucent. If the aircraft is between you and the nearest light source you can see the shapes of the internal framework through the canvas, and components between the canvas and the light show up in silhouette. Modelers have come up with various ways to suggest that on opaque plastic parts, usually by shading the areas around the ribs with a slightly darker hue.
Here's a source of information that may not be well known. In observance of the 100th anniversary of the first flight, the university where I work sponsored a research project in which a fine historian, Larry Tise, took an extremely careful look at the documentary and photographic information regarding the Wrights - with emphasis on the time they spent in North Carolina. The university library created an online "digital exhibition" of documents and photos, including quite a few that have never been published. Here's the link: http://www.lib.ecu.edu/exhibits/wright/index.html . For the most relevant photos, click on "Photos," then on "Hidden Images." In Photo #669, see if you can figure out the "unknown reason" why Wilbur is "distancing himself" from the Flyer just before the first flight. I must say it seems fairly obvious.
The famous photo of the Flyer lifting off the ground for the first time has been reproduced so many times that few people pay close attention to it any more. It's usually reproduced with severe cropping - which takes out some of the most interesting features. Once you start studying it carefully it becomes one of the most fascinating pictures in the history of aviation. The print on the ECU site shows the whole frame, including the broken corner of the original glass plate negative. (For an even better impression, make a pilgrimage to the Air Force Museum, at Dayton. The folks there have blown up the uncropped image to the size of a wall.) Interesting points include the pattern of footprints around the place where the aircraft started (you can just about make out the outline of the wings), and of the footprints Wilbur made as he ran alongside holding the wing, then peeled off to the right.
The links in the "Further Reading" section of the ECU site are also worth following - especially the one for the Library of Congress. That one has some nice, closeup photos of the original engine. Its overall color pretty clearly was unpainted aluminum.
Reproducing the appearance of that great machine in model form is quite a challenge. Hope this helps a little.