Marcus is color-blind because he lacks cone receptors for wavelengths of light in the red spectrum. Marcus's inability to see the color red illustrates a deficit in the process of .

The correct answer is: Sensing capability.

Explanation:

The inability of a person to detect red colour is known as Protanomaly.Humans are able to sense colours due to the presence of cone cells in the retina of the eye.Cone cells are specialised for detecting colour.A person affected with Protanomaly, lacks the red colour detecting cone cells in their retina.Their brain is unable to understand red colour because the sensory impulse for recognising the red colour is not send from the retina of the eye to the brain through the optic nerve due to the absence of the red colour detecting cone cells.Hence, Marcus is colour blind as he lacks the capability of Sensing light in the red region of the spectrum.

Ais the correct answer