As Bryan suggests, thin ply. For a scale appearance, pick one with little or no grain at all. Alternatively use thin lime wood (box wood) as it has almost no grain.
The point of no grain is that at scale sizes the grain would be almost invisible.
You can then stain the wood to the correct colour, or use coloured varnishes.
For a working boat, I suggest you do not go for a perfect finish and perfect colouration, it makes the boat look unatural. For a yacht perfection is often seen on the full size boat (but not always) so may be more in keeping.