We are going to do something interesting, if we look at the head of the black man as we see it in the painting, with the white collar, and if we look at it without the collar, we will see two very similar heads, but with some differences.
The differences are the nuances that we can see if the white collar, which reflects a lot of light towards our eyes, is eliminated. Without that collar, the face has more nuances.
Of course, in a museum, with the special lights, and directed towards the painting, so that it passes through the layers of paint, the light reaches the white preparation of the fabric, and is reflected up to our eyes, showing us all the subtle colors of the paintings, and the various layers of paint, with their oils and varnishes or resins, which increase the transparency of the layers, and therefore the luminosity of the reflected light ...
In the original painting we would see a beautiful black man's head, with more accentuated lights and shadows ...