how do I do "woodgrain" on fondant planks?

You can mix some brown and yellow gel food color with somealcohol or lemon extract and paint it lightly with a paintbrush till you get the effect you like. You can also mix white and chocolate fondant together and knead until its marbelized. Roll out and it looks like natural wood. I have a picture of a cutting board in my pics, thats how I did it. HTH

you can do woodgrain a few ways or a combo of all of these.

start by having different colors of brown/tan/ivory/orangey browns/etc. and have a little bit of each color and twist them together and fold them over a few times til when you roll it out, it looks like the different grains in a piece of wood.

from here, you can cut them into rectangular planks. or you can buy a woodgrain impression mat and roll that on top of the fondant and voila...instant dents where you need them! add "nails," shading, door handles etc. for whatever you are trying to make!

hope this helps!