Hooo boy. This is a pretty complicated topic. I'd better start with the large caveat that I've never done much research about the French navy. I've got quite a few books about British practice, but not as much on the French. So take the following with a large grain of salt.
I've bumped into several articles about
La Flore over the years, but I'm afraid my senile brain doesn't remember much about them. I do remember that there were at least two French frigates of that name. A book I happen to have at hand mentions a
Flore that was launched in 1728, but I think the one represented by the Lindberg kit is a later ship - from about the time of the American Revolution.
My guess is that the topside planking was unpainted, but treated with some sort of oil as a preservative. Contemporary paintings show unpainted hull planking in a variety of shades, ranging from light beige to dark brown. Some folks have suggested that the variation was connected with the aging of the oil treatment; that it started out almost transparent and turned almost black as it got older. I have my doubts about that one, but you can paint the above-water hull almost any shade of brown you like and few will be able to argue.
It seems to have been customary to treat the wale - the belt of thick planking just above the waterline - with a darker-colored substance (probably tar, perhaps with something else mixed in with it). Most contemporary pictures seem to show dark - almost black - wales, and the documents (at least the British ones) contain lots of references to "tarring the wales."
The underwater hull is a trickier subject. In
La Flore's day both the British and French navies were in the process of adopting the copper-sheathed hull, applying copper to the bottoms of ships when they were in drydock facilities. I have a general impression that the British were a little ahead in the race. (At the Battle off Cape Henry, Virginia, on March 16, 1781, five of the seven British ships-of-the-line had copper bottoms; three of the eight French ones were coppered.) But I have no idea when - or if -
La Flore got a copper bottom.
If I remember correctly (I haven't seen the kit for many years), the Lindberg mold makers didn't provide any indication of copper sheathing but put raised lines on the underwater hull to suggest the edges of the planks. That may well be correct. If you want to represent an un-coppered hull of the period, there actually are several options.
The general practice prior to the introduction of copper sheathing, especially if the ship was headed for a tropical climate (where the teredo worm would be a menace), was to paint the underwater hull with an repulsive substance containing tar and horse hair, and then nail on a layer of thin "sheathing planks." That treatment was supposed to discourage the worms. (It certainly would have that effect on me.) The sheathing was then painted with one of several concoctions that were intended to discourage the growth of weeds and other parasites. "White stuff" was a mixture of train oil, rosin, or sulphur, sometimes with a coat of tallow applied on top. The overall appearance of it probably was a slightly yellowish off-white. Brian Lavery, one of the senior current experts on the subject, says that "black stuff," a mixture of pitch and tar, was actually more common - at least in the British navy during the first half of the eighteenth century. In about the 1740s, Mr. Lavery says, a third treatment came into use: "brown stuff," which was "black stuff" with the addition of sulphur.
Just how any of this stuff actually looked - especially after the ship had been in the water for some time - is an interesting question. A really accurate rendition of an uncoppered hull that had been submerged in salt water for several months would not be something I'd care to put in my living room. Some modelers deal with that problem by simply painting the underwater planking white. (That approach is quite common among the beautiful contemporary "Board Room" models.) Another approach, which I happen to like, is to paint the planking an off-white color and gently "weather" it with dry-brushed strokes of slightly darker shades of grey, beige, and green. To my eye that gives at least an impression of a hull that's been in the water for some time - without involving me in the scale reproduction of barnacles and seaweed.
That's how I painted the bottom of my little model of the Continental frigate
Hancock. Here's a link to some pictures of it: http://gallery.drydockmodels.com/hancock . I'm afraid none of these shots shows the bottom really clearly, but they should give at least a hint of what I was aiming at. (The topsides of this ship, incidentally, are known to have been painted yellow.)
One of the great aspects of sailing ship modeling, in my opinion, is that it allows more range for personal taste than most other forms of scale modeling. Those old ships didn't follow rules like modern ships, airplanes, and tanks do; sailing ship modelers don't talk in terms of Federal Standard color numbers and camouflage measures. My suggestion for any sailing ship modeler is: do all the reading you can to find out what the real ship looked like, and when the reference material runs out, do what looks best to your own eye.
Hope this helps a little. Good luck. It's a great hobby.