A person with colour blindness typically has difficulty in distinguishing between which pair of colours?

Introduction / Context:
Colour blindness is a common inherited condition that affects how people perceive colours. It is frequently discussed in biology and general science because it is linked to genetics and the structure of the eye. The most common form of colour blindness affects the ability to distinguish certain colours. This question asks which pair of colours is typically difficult to distinguish for a person with colour blindness.

Given Data / Assumptions:

• The topic is human colour vision and colour blindness.
• The options list different pairs of colours: green and red, white and red, blue and red, and red and black.
• We assume standard school level information focusing on the most common type of colour blindness.
• We are not dealing with rare types of colour vision deficiency.

Concept / Approach:
The most common type of colour blindness is red green colour blindness, which includes conditions such as protanopia and deuteranopia. In these conditions, the cone cells in the retina that respond to red or green wavelengths are absent or not functioning properly. As a result, people have difficulty distinguishing between shades of red and green, especially when the colours are similar in brightness. White and red, blue and red, or red and black are much easier to distinguish because they differ greatly in both brightness and hue and are not typically confused in common forms of colour blindness. Therefore, the pair green and red is the correct answer.

Step-by-Step Solution:
Step 1: Recall that normal human colour vision depends on three types of cone cells, sensitive to red, green, and blue light. Step 2: In red green colour blindness, the red sensitive or green sensitive cones are missing or not working properly. Step 3: This leads to difficulty distinguishing colours in the red and green range of the spectrum because their signals overlap or are absent. Step 4: White and red are very different in brightness and are not commonly confused, and blue and red use different cone cells that are usually intact in red green colour blindness. Step 5: Therefore, the classic pair of colours that colour blind individuals struggle with is green and red.

Verification / Alternative check:
Most educational materials and eye test charts for colour blindness focus on red and green patterns. Special plates called Ishihara plates use dot patterns in red and green shades to detect red green colour vision defects. These tests do not compare white with red or red with black, because those differences would be obvious even to a colour blind person. This practical testing approach strongly supports the fact that difficulty distinguishing red and green is the hallmark of common colour blindness.

Why Other Options Are Wrong:
White and red is wrong because white is essentially a mixture of all wavelengths and has a very different appearance from red, making it easy to distinguish even with colour vision deficiency. Blue and red is incorrect because problems with blue perception are relatively rare, and red green colour blindness mainly affects the red and green cones. Red and black is also wrong since black is the absence of light and looks very different from any coloured light, including red, so confusion between red and black is not typical of colour blindness.

Common Pitfalls:
Some students may pick other colour pairs simply because they look strikingly different to them and they assume this might be hard for others to see. Others might not recall which specific colours are involved and make a random guess. To avoid this, remember the key phrase red green colour blindness that is repeatedly used in biology textbooks. Linking colour blindness directly to green and red in your memory makes it easy to answer similar questions accurately.

Final Answer:
The correct choice is Green and Red, because the most common form of colour blindness affects the ability to distinguish these two colours from each other.