Hi Beau,
Yamato spent her entire life painted in Kure Grey, including her steel decks. She also had some decks covered in linoleum, so you'll need that as well. In our Colourcoats enamels, that would be:
IJN 02 Kure Grey and IJN 10 Linoleum.
Her wood decks were unpainted Hinoki cypress, up until the Battle for Leyte Gulf, at which time they were stained (not painted) black; they were also stained black for her last sortie toward Okinawa. For Hinoki cypress, use our RN 20 Late War B55. For black-stained decks I'd go with a very dark neutral gray like our ARG 08, Anthracitgrau.
Cheers,
John Snyder, White Ensign Models, http://WhiteEnsignModels.com