Australopithecines didn't need to be dark. They had fur.
The display in question at the Chicago Museum of Natural History, if I remember correctly, did not go back to australopithecines, although it was labeled "the dawn of man." There was one diorama, the first in the series, of a couple of hairy ape looking (supposedly humans) sitting around a fire, but I don't think they were australopithecines, because I remember them as being the size of modern humans. I believe the earlier humans were generally shown as darker skinned. It's possible this was a source of racist accusations, but the display featured cultural evolution as much as it did physical, and each display showed a cultural progression like hunting, domestication of animals, the beginnings of agriculture, the advancement of art, and development of advanced tools.
I questioned the racist accusation, because I would have criticized it more on inaccuracies due to recent additions to our knowledge base. The display was there in the 1940s, so was probably designed way before at a time when anthropologists were just beginning to piece our history together. It probably included species that are now known to be outside our direct lineage. In addition, so much has changed since the 1960s when I took anthropology courses, that my guess is that it simply became outdated.
It's been replaced by a fairly well done display focusing on australopithecines, but avoids the more daunting task of speculating about man's evolution beyond that.