These are the dolls they used in that test. https://www.history.com/.image/t_share/MTU3ODc4NjAyOTg5OTA1MjI1/image-placeholder-title.jpg

Both baby dolls are not very aesthetically pleasing to look at but the black baby's reddish brown eyes look menacing from the bright flash of the camera. I think if you want to do an accurate doll test you need dolls that match the aesthetic ideal of a baby of each race. You would need focus test groups of blacks and whites for the ideal doll of their race and probably need multiple options instead of a binary choice. Most of the tests that attempt to show self-loathing of other races use palette swaps of images and dolls for their experiments. Race is more than skin color and the facial structure probably matters more and I would not be surprised if the children choose the doll that appears to be similar to them.