Planeguy,
Welcome aboard it's nice to have you here. What make of the Bismarck are you working on? Also, you will find that this questions has a many answers and everyone usually has their own methods.
You might want to do some research on wooden decks on the internet so see the different colors decks can be. One thing to remember is that wood on a ship's decks do not stay a "wood" color for long. The sun and salt water as well as salty air grays them out fairly quickly. So that a slight greenish gray or other tones of gray, depending on the wood used, is pretty much the color of the decks. Another factor is how often the crew washes/cleans the decks will give it different tones from a light gray to a dirty gray.
If you want and even one tone paint job, I would suggest Tamiya Wooden Deck Tan TS-68 which is a spray can. If you want something a little more realistic, but still one tone, then Tamiya Deck Tan XF-55 or Vallejo Deck Tan 986. I would airbrush the Tamiya but you could do either with the Vallejo. Another brand you can airbrush or brush is Model Master Aged Concrete which is an old Floquil color which unfortunately I do not have the number of.
If you are really up for it, then you can mix up 3 batches of say the Vallejo Deck Tan. One batch is the regular color, one you will want to add some white to lighten it up and the third batch you will want to add some brown, dark gray or just a tad bit of black to darken it up.
First you will want to paint the deck the regular color. When that dries, then the fun part begins. Take the tape and cut strips of different lengths and cut to the width of the planks on your Bismarck. Randomly place them onto the planks and then spray or brush lightly your darker color. When that dries, tape those off and then use you lighter color on the remaining planks. After that is dry, take the tape off and then if you have an airbrush lightly spray a mist coat of the lighter color to tie everything together. This method is not for the faint hearted but it is a method that really makes your decks look good.
As I said, there are many ways to paint your deck and you should do whichever matches your skill level. Hopefully I didn't make too many typos…..
Good luck,
Steve