What is the photopigment associated with a M cone?

The photopigment associated with M cones, which are responsible for medium wavelength light perception, is chlorolabe. Chlorolabe is particularly sensitive to wavelengths in the green region of the spectrum, allowing M cones to contribute to color vision, especially in differentiating green hues.

In visual perception, different types of cones are associated with specific photopigments that absorb specific wavelengths of light, enabling the perception of color. The S cones, for example, contain cyanolabe, which is sensitive to the blue spectrum. The L cones are associated with erythrolabe, which is sensitive to long wavelengths or red light. Photopsin refers to the general class of photopigments without specifying the type, and retinaldehyde is a component of all photopigments involved in the visual cycle, not specific to any cone type. Therefore, chlorolabe is the correct answer as it is the specific photopigment responsible for the function of the M cone.