Without questioning the beautiful Sinterklaas festival, and far away from agitation and street cult, here is something to explain what might be against Piet's black.
As you often hear, children have no problem with a different color for Piet. They will therefore not have much trouble with me a white Piet. No, it is rather the adults who want to stick to the tradition of black.
That is remarkable, because when the tradition of one Piet faded and more Pieten appeared at the Saint at the same time, it gave much less resistance. Also, the tradition of a saint who threatens children with the roe and take them in the bag quite silently released. But now that it's all about color, it's different. There the arrival of migrants and uncertainties due to globalization will not be strange.
So it requires an extra effort to understand what is so against the black of Piet. Most Dutch people are nice people who mean nothing bad with Piet's black and Saint's white. And they do not want to be a parent at all. But if they have white skin, they can be the parent in the eyes of people with a different skin tone. To those people, white Dutch people listen with respect to understand how underlying parties feel.
After all, it is known that parent parties often do not know that much about it. The underlying party must know what is going on in the other party. The parent party has that need much less. That is the difference. As a result, many white Dutch people, well-disposed as they are, underestimate the damage that Piet's black can cause. This damage occurs when children look at a subordinate, walking servant who is black and a boss with a high hat on top of a horse who is white.
Children learn from this image that black is inferior and that white is of a superior quality. They take that unfortunate distinction into their lives. The assumption that small children do not pick up the unfortunate image arises from an underestimation of our unconscious. But there is a lot of commitment in the unconscious of small children. Those early fixings in our brains determine to a large extent what we observe later and which explanation we give them. Science emphasizes that dominant role of our unconscious.
Perhaps the creeping pain does not apply to everyone with a dark complexion but to many of them. Why would not we want to prevent their pain by giving Piet and Saint the same skin color?
PS. Behind the scenes I get appreciation from people with darker skin. They would rather not talk about it in public, but are happy if someone else does.