## **Core Concept**
Colour vision is a complex process that involves the detection of different wavelengths of light by specialized cells in the retina, known as **photoreceptors (rods and cones)**. The perception of colour is primarily mediated by **cones**, which are sensitive to different parts of the visible spectrum.

## **Why the Correct Answer is Right**
The correct answer, **cones**, is right because cones are responsible for colour vision. There are three types of cones in the human retina, each sensitive to different wavelengths of light: **long-wavelength cones** (sensitive to red light, approximately 600-700 nm), **medium-wavelength cones** (sensitive to green light, approximately 500-600 nm), and **short-wavelength cones** (sensitive to blue light, approximately 400-500 nm). The signals from these cones are processed in the brain to create the perception of a wide range of colours.

## **Why Each Wrong Option is Incorrect**
- **Option A:** is incorrect because, although rods are a type of photoreceptor, they are not primarily responsible for colour vision. Rods are more sensitive to light and are used for vision in low light conditions but are not sensitive to different wavelengths of light in the same way cones are.
- **Option B:** is incorrect because it seems to imply another type of cell or structure not directly related to the primary detection of colour. Without a specific term, it's hard to address directly, but generally, colour vision is attributed to cones.
- **Option D:** is incorrect because it likely refers to another structure or cell type not directly involved in the initial detection of colour.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **colour blindness** is usually inherited and affects males more frequently than females due to the genetics of the X chromosome, where the genes for the red and green light-sensitive cones are located. A classic clinical test for colour vision is the **Ishihara test**, which uses dots of different colours to form numbers that people with normal colour vision can see but those with certain types of colour blindness cannot.

## **Correct Answer:** . cones