Hi John,
Although, I seem to have no trouble with seeing a No. 2 pencil line on dark walnut, I have a collection of Rexel Derwent Studio color pencils, which write very clearly on wood. The Chineses white and other light colors work very well. The only draw back is they dull quickly and have to be sharpened frequently. Derwent pencils are usually available at art stores.
dave