Whether the rug manufacturer used synthetic dyes or natural dyes to make the rug might be a subtle difference, but one worth noting. Below is an excerpt from Rug News in which Peter Davies helps to clarify the difference between synthetic and natural dyes.
"Under an electron microscope, a wool fiber dyed with natural dyes has more of a speckled rather than a solidly colored appearance. As a result of these microscopic differences, the human eye perceives the natural dyed yarn as soft and muted. Conversely, the eye perceives wool dyed by synthetics as harsher, more aggressive, more extroverted in character…
“Not only do natural and synthetic dyes take differently to wool, but there are also important differences in the way natural and synthetic dyes are perceived by the human eye and brain. If, for instance three strands of wool are each synthetically dyed red, blue and yellow and placed side-by-side, the effect of the combination will be disharmonious. Whereas if three strands dyed indigo blue, madder red, and milkweed yellow are similarly placed, the effect will be quite harmonious. It is precisely because natural dyes are impure, and therefore reflect a broad range of wavelengths, that harmonious combinations are more possible. It is the overlapping of the hues that make for color harmony..."