I have found that Humbrol #63 (Sand) has got me closest to the sorts of hues that appear on British ships in the American War of Independence in the paintings of contemporary artists like Dominic Serres, Thomas Luny and Nicholas Pocock. I am not sure how much I can trust paintings (which attract dirt over time) or contemporary ship models (which were built to show the design, not the exact colour). I have not tried to find a ‘perfect’ match as I imagine there was a fair amount of variation between ships of different ages anyway.
Here are a couple of pictures of mine so that you can judge for yourself.
Sultan in the picture above is not in Humbrol #63; the others all are. I no longer paint sails in white.
The British ships here are meant to be in unpainted wood. The French are mostly in a ‘double striped’ scheme with various shades of brown.
So I think you are looking for a shade (or several shades) of dark yellow to golden brown to represent unpainted wood.
Good luck. I look forward to seeing your results. 🙂