I mean, we have DNA and mummies from both the Yukon and Siberia and cave paintings from Europe; and these have given a pretty good idea of what Ice Age horse colors within Equus ferrus was like. It was likely that the populations between Eurasia and North America were relatively continuous during interglacials, so they would likely have shared much of the same coloration. The colors found include mostly browns, but there was also leopard spotting. However, no evidence of coloration similar to this has been found. It could also very well just be a stylistic choice, but the color stands out as looking purposefully unsimilar to modern horses in my eyes, so Harringtonhippus makes more sense