I thought there was evidence of Southern influence into the Yamnaya culture. Wasn't there more recently a study which said that the Kurgan burial system has it's roots somewhere in Mesopotamia or Northwestern Iran?
Kurgan people were darker skinned than modern people from that area, but not in the way Hunters and Gatherers were (very Dark skin + light eyes) but in the way that they likely had Olive like skin and mixed but mostly brown eyes?
The Hunters and Gatherers were not "dark skin and light eyes", cro-magnons were all brown eyes and dark skins, if I don't do mistake, there are just one example, it's Labrana, and he has just 50% chance to have light eyes, he could have been also brown eyed. In my opinion, the presence of light eyes during the late mesolithic (5000BC) could be easily explained by the presence of IE in Europe (in the east part), and R1b was probably already present in the west part, remember Labrana was supposed to have "scandinavian genes" (sorry I don't remember the term), but he have been found in...Spain. I think to make generality with one case is not judicious imo.
For the recent kurgan peoples, Eurogenes has an interesting article and show some of the problems of the study (sorry I can't post the link), and why they has brown eyes and olive skins:
"Surprisingly, the article doesn't mention Keyser et al. 2009, a very important study which showed that a sample of Kurgan nomads from Bronze and Iron Age South Siberia had frequencies of light hair and eyes comparable to those of present-day Northern and Eastern Europeans. Also worth noting is that the most common Y-chromosome haplogroup among these individuals was R1a, which is today the most frequent haplogroup in Eastern Europe, including Ukraine. What this suggests to me is that the Kurgan cultural horizon was not genetically homogeneous. I suspect that Kurgan groups closer to the Balkans carried significantly higher levels of Near Eastern Neolithic farmer ancestry, and were thus much darker than those in the more temperate northerly regions. However, it seems that at some point, the Neolithic farmer DNA was diluted enough by continuous movements of light pigmented groups from the north and east, possibly made up mostly of males, that there was a major shift in pigmentation traits from Near Eastern-like to Northern European-like across most of Eastern Europe. This scenario actually fits very nicely with the latest on the genetic origins of Europeans."
And if I remember correctly, we don't have the Haplogroup Y of these study, so it's not really complete (they could have been mixed).
For the physical aspect of the original IE, imho, that very clear, between all the examples we have, the Andronovo peoples, the Scythians, the Tocharians, the Yuezhi, and the IE of Europe; well they were all, physically europeans, with light hairs and eyes; we have a big majority of IE with these physical features that the opposites, despite that these IE peoples were geographically separate since 1000 years for some of them (sorry for my english).
Except that, thank you very much for ebAmerican and Mattbir for to post the historical facts by archeologists expert, that don't let the place to speculation imho, and thank you also for Polako for your great posts.