zwarte piet came at a point just after slavery was outlawed throughout colonies of the empire, the sinterklass character was more of a bogyman type, who would come and take children who were bad away to Spain( Netherlands enemy). the Zwarte piet character was a helper for this bogyman type, piet would climb down the chimneys of the bad kids and take them away. The whole story conditions children to associate's zwarte piet with evil and being bad. The clothes, black face, big red lips and gold earrings, these ware all typical depictions of the stereotypes of the time.
Yes things have changed over time and the story and been bent to hide certain aspects but this zwarte piet character was still conceived at a point where racism was rife in western cultures.......