Immediately after this first sentence of Part I, the narrator tell us that
Their eyes glanced level, and were fastened upon the waves that swept toward them. These waves were the hue of slate, save for the tops, which were of foaming white, and all of the men knew the colors of the sea . . . These waves were most wrongfully and barbarously abrupt and tall, and each froth-top was a problem in small-boat navigation.
In other words, the four men in the boat have quite enough to think and worry about, and their attention is completely and totally consumed by their contemplation of how to handle the terrible waves that move, relentlessly, toward them. They all know the color of the waves, the narrator says, because the waves are what pose the danger to them at present, not the sky. Further, these waves are characterized as wrongful and barbarous, as though they are hurled purposefully at the men by some uncaring and insensitive force. This force, as we learn throughout the story, is Nature, and it does not matter who is the hardest-working or the most deserving, or that the men are innocent of wrongdoing, or that their lot is somehow unfair; Nature is not fair. The horrible waves that prevent the men from even lifting their eyes momentarily toward the sky prove it.