The answer to your question can be found in a text which also quotes Gauguin himself. See paragraph describing a nearly naked man wielding with both hands a heavy axe that left, at the top of the stroke, its blue imprint on the silvery sky and, as it came down, its incision on the dead tree, which would instantly live once more a moment of flames -- age-old heat, treasured up each day. On the ground purple with long serpentine copper-coloured leaves," ..... these are the "brown things" that you mention.
And he also describes "the woman stowing nets in the pirogue (that is a canoe), and the horizon of the blue sea was often broken by the green of the waves' crests against the coral breakers" As you read this scene represents for him the whole mystery of life in Tahiti. This picture was then for sale, and this is a description of it - a little difficult to read - but worthwhile. As you will note the pose of the woodcutter on a figure on the west frieze of the Parthenon, Greece.
