>>513382256
The pastoral groups of Chad and east of it (Nilo Saharans) have the blackest skin in the continent. DESPITE them having substantial Eurasian ancestry, they are still darker than Yorubas.
The East: Siberians have darker skin than the Northern Chinese, despite being much further north--for the exact same reason (the latter are agriculturally adapted).
We also know that light skin has a disadvantage in sun: folate depletion. Staying in sunlight depletes folate. An outdoor lifestyle (steppe) would deplete much more folate than a sedentary lifestyle (farming, settled fishing, settled dairy).
Many dark skinned races also literally cannot synthesize vitamin D from the sun, look it up. Modern whites need only 10 minutes in summer sun to create a full day's worth of D. A dark skinned person can sunbathe for 3 HOURS and still barely make a dent. Thus, sunlight is not a significant source of vitamin D after a certain level of skin pigmentation.
To combat this, most dark skinned races have genes which are cause endogenously high vitamin D levels irrespective of sunlight exposure. The Yamnaya were 90% positive for such a mutation. Modern whites are about 20%. rs7940244.
In general, ceterus paribus:
steppe = darker, settled = lighter
fish = darker, meat = intermediate, lactoveg = lighter
equator = darker, poles = lighter
Yamnaya were steppe, meat, and more southerly than the peoples they conquered.