Final answer:
Humans lack distinct cone types for the color indigo; instead, they have three cone types that work together to perceive a range of colors through trichromatic vision.
Step-by-step explanation:
Humans do not have distinct cone types to respond explicitly to the range of light wavelengths associated with the color indigo on the visual spectrum. Human vision relies on a trichromatic system composed of three types of cones that are sensitive to different wavelengths of light. These cones are named S cones (short), M cones (medium), and L cones (long), which are most responsive to the wavelengths approximately 420 nm, 530 nm, and 560 nm, respectively. As such, the color indigo at about 450 nm is not the peak sensitivity for any of the three types of cones but is between the S and M cones' sensitivity ranges. The human eye perceives colors through this system by comparing the activity of these cones and processing the combined signal in the brain to experience the whole spectrum of colors.