Answer:
Talks like this, a green wise man does. Guess my clue, you will.
Salty water everywhere but not sea in sight.
I scribble forms of the finest letter, And repel elements of the harshest weather. I am an arrow-aimer and a dust-breaker.
A harvest sown and reaped on the same day In an unplowed field, Which increases without growing, Remains whole though it is eaten Within and without, Is useless and yet The staple of nations.
Brown I am and much admired; many horses have I tried; tire a horse and worry a man; tell me this riddle if you can.
Black we are and much admired. Many seek us if they are tired. We tire the horse, and comfort man, and turn White when we've fulfilled your plan.