* Pigment: Hair color is determined by two types of melanin: eumelanin (responsible for brown and black) and pheomelanin (responsible for red and yellow). Blond hair has very little eumelanin and a small amount of pheomelanin. Red hair has a significant amount of pheomelanin and often a small amount of eumelanin.
* Darker Appearance: While pheomelanin itself is reddish-yellow, a higher concentration of it in red hair usually results in a darker and richer color than the diluted effect of pheomelanin in blond hair.
That said, hair color is a spectrum. There can be very light shades of red hair (strawberry blond) that are lighter than very dark shades of blond hair. However, *on average*, red hair is darker than blond hair.