This question is very interesting to me because I have a foot each in the world of the colonizer (I'm American, half-white) and the colonized (My father is a native Filipino, born and raised there. Also, I lived all of my childhood in Micronesia). So questions of how the colonizers and the colonized relate to each other are interesting to me.
Personally, I do not think that these paintings by Gauguin show postcolonialism. Instead, I would say that postcolonialists would criticize Gauguin's paintings. They would say that his paintings are from the point of view of the colonizer.
Postcolonialism is supposed to show that colonized people are not all the same. It is supposed to rethink the relations between the colonies and the colonizers. But I think Gauguin's work stereotypes the colonized people he paints.
Gauguin's Tahiti paintings are all in a primitive style, as if emphasizing that the Tahitians were different from and less civilized than Europeans. They also mostly show women and children, most of whom are at least partly naked. To me, the nudity emphasizes that Tahitians are backward and invites us to think of them as sex objects. In addition, I think that Gauguin's choice to only show women and children implies that Tahitians are not strong.
All of this is in line with colonialist ideas, not postcolonialist ones.
The artist Paul Gauguin was a cultured European artist who traveled to Tahiti where he became infatuated with the indigenous people of Tahiti. When he moved to Tahiti he was looking for an escape. He had been struggling to make a living as a painter after giving up several lucrative positions and his wife and family. He hoped in Tahiti that he would find no need for money and that he could live a simple life. Tahiti had already been colonized by the French prior to Gauguin’s arrival. Initially what he found on his arrival was a colony of Europeans that had brought their culture and life styles with them. He made the decision to move away from the cities and live among the indigenous people. He resided in a hut. He was interested in the primitive parts of the Tahitian life and avoided the colonies. He hunted, fished, and lived among the native people learning from them and admiring them.
The paintings Gauguin created in Tahiti were more natural and had smother lines. He stopped imitating other styles and his own presence began to emerge in his art. He painted some of his series with Christian undertones, still hanging on to his upbringing, but eventually began to put the natives in his paintings in their own world and ideals. He allowed their innocence and beauty to flow onto the canvas. However, it is important to note that when Gauguin painted many of his scenes of primitive worship of idols in his Tahiti paintings, the Tahitians had long before given up many of the practices due to the influence of the French.