What aspect of pheomelanin contributes to its color variation?

The color variation in pheomelanin is primarily influenced by genetic factors. Pheomelanin is one of the two main forms of melanin, the other being eumelanin, and is responsible for the yellow to red hues observed in hair and skin. The specific genes that are expressed can dictate how much pheomelanin is produced and its composition, leading to variations in color.

Different genetic variations can result in differing amounts of this pigment, which can produce a range of colors from light blonde to deep auburn. Therefore, the genetic makeup of an individual plays a crucial role in determining the specific traits and characteristics of their hair color, which is the primary reason why choices related to pH level, hair thickness, or the presence of sulfur do not adequately explain the color variations seen in pheomelanin.