Answer :
Answer: b. His retina is void of at least two types of cones.
Explanation:
The cones are the cells present on the retina that are responsible for identifying the color of the object without cones the person is not able to identify or distinguish between colors of the same type.
The achromatopsia is a condition which is a kind of color blindness. In this condition a person can only see black, white and shades of gray. This occurs due to the fact that the retina is void of at least two kinds of cones that are white or black. The color vision deficiency may vary from mild to severe which depends upon the whether the color blindness is inherited or because of injury or illness.
According to the given situation, Matteo is suffering from the color blindness thus is able to observe black, white and shades of grey thus may be because of the fact that retina is void of atleast two kind of cones that is white and black.