Colour blind people are unable to differentiate

The correct option is A Red and green colour
Colour blindness is the inability or decreased ability to see colour, or perceive colour differences, under normal lighting conditions.The different anomalous conditions are protanomaly, which is a reduced sensitivity to red light, deuteranomaly which is a reduced sensitivity to green light and is the most common form of colour blindness and tritanomaly which is a reduced sensitivity to blue light and is extremely rare. People with deuteranomaly and protanomaly are collectively known as red-green colour blind and they generally have difficulty distinguishing between reds, greens, browns and oranges.

Therefore, the correct answer is option C.