From “Ancient DNA Provides New Insights Into Cave Paintings of Horses” (ScienceDaily, Nov. 7, 2011), we learn:
The team, which includes researchers from the University of York, has found that all the colour variations seen in Paleolithic cave paintings — including distinctive ‘leopard’ spotting — existed in pre-domestic horse populations, lending weight to the argument that the artists were reflecting their natural environment.
The dappled horses’ spotted coat pattern bears a strong resemblance to a pattern known as ‘leopard’ in modern horses. However, as some researchers believed a spotted coat phenotype unlikely at this time, pre-historians have often argued for more complex explanations, suggesting the spotted pattern was in some way symbolic or abstract.
Apparently, the horse genes were there for “leopard” spotting, contrary to what some have supposed.
So the cave painters were just as likely drawing from life.