Well, unfort unately, there's no simple answer to that. Fresh, varnished teak is a rich, slightly orange-ish brown. Here's a link to some pictures (with the usual caveat that colors on monitors aren't entirely reliable): http://216.105.59.114/index.asp?PageAction=PRODSEARCH&txtSearch=teak&Page=1
(That website, incidentally, is Constantine's, a fine supplier of all sorts of wood-related materials. Worth some browsing.)
There are, of course, variations. Lots of well-maintained, varnished teak that I've seen on boats isn't quite as orange-ish as the pictures suggest; it's closer to walnut. Carefully-maintained varnish makes teak stay that color almost indefinitely. If it isn't varnished, though, it fades rather quickly to a nondescript, slightly silvery grey color. Here in my office I have a chunk of teak that was once part of the maindeck of the yacht Atlantic, the three-masted schooner that won the Kaiser's Cup in (I think) 1919 and still holds the record for crossing the Atlantic under sail alone. I got the deck fragment when she was being broken up; she'd be falling to pieces next to a pier in Norfolk, Virginia for quite a few years, and the piece I've got may in fact have been underwater. It still does have a noticeable brown cast to it, but if you had to label its overall color you'd almost certainly call it grey.
Except on extremely small parts, no single color will make styrene look much like unpainted wood. A good way to create the illusion is to start by painting the surface in a color that matches the lighter portions of the wood (in this case a rather light brown with quite a bit of orange in it). Let that dry. Then mix up a much darker brown, in the form of a thick blob on a palette or a scrap of paper. Dip the very tip of one finger in that mixture and rub it gently along the plastic, in the direction the wood grain would be running. With a little practice, you'll be surprise at how much the result resembles wood. To enhance the effect, try using a third color in an in-between shade.
I can't offer any specific paint numbers or mixing ratios. This sort of thing really needs to be done by eye. (There aren't any "official" colors for sailing ships. Aircraft and tank modelers talk in terms of FS Numbers or Methuen Numbers; sailing ship modelers don't. Thank gawd.) And every modeler has his/her favorite paint brand. Mine is PolyScale acrylic; other modelers prefer other brands. Testor's has recently issued an interesting range of colors blended especially for ships in its "Acryl" line. Model Shipways also sells a line of acrylics specifically intended for sailing ships. All those colors are educated guesses, though. There's no "right" or "wrong" color for a ship model.
My suggestion (assuming you have access to a reasonably well-stocked hobby shop - not a safe assumption these days, unfortunately) is to take a look at the range of colors in the line you like best. Pay particular attention to the browns, yellows, and reds. Don't pay any attention to the color names. You don't care whether a particular paint bottle is labeled "Soviet Air Force WWII Red-Brown," "Burnt Sienna," "German Panzer Yellow," or "Union Pacific Depot Buff." What counts is what the color looks like. Buy a few colors and start experimenting. Take a look at the photos of real ships on the web, and the paintings of the old master marine artists. If you have the opportunity, go visit a restored ship or two. (Take those with a grain of salt, though. Remember that modern paints and wood treatments don't necessarily look like those of previous centuries.) When the colors on your model look right to you, they are right.