Colour blindness in which all colours appear grey is?

The correct option is A Monochromatism

1) Monochromatism is the total inability of a person to perceive colour. A person with true monochromatism perceives only black, white, and shades of grey. It is due to lack of or damage to the cones of the eye that perceive color, or to inability of the nerves to translate information received from the cones.

2) Dichromatism is a form of colorblindness in which only two of the three fundamental colors can be distinguished due to a lack of one of the cone pigments.

3) Blindness to red is known as protanopia, a state in which the red cones are absent, leaving only the cones that absorb blue and green light.

4) Blindness to green is known as deuteranopia, wherein green cones are lacking and blue and red cones are functional.

So, the correct answer is 'Monochromatism'.