**Core Concept**
Colour vision is a complex process that involves the perception of different wavelengths of light by specialized photoreceptor cells in the retina. In humans, this is mediated by the interaction of light with specific types of photopigments in cone cells.

**Why the Correct Answer is Right**
Cones are the photoreceptor cells responsible for colour vision in humans. There are three types of cones that are sensitive to different parts of the visual spectrum: long-wavelength cones (L-cones) sensitive to red light, medium-wavelength cones (M-cones) sensitive to green light, and short-wavelength cones (S-cones) sensitive to blue light. The signals from these cones are transmitted to the brain, where they are interpreted as different colours. The specific combination of signals from L-cones, M-cones, and S-cones determines the colour perceived by the individual. The rod cells, on the other hand, are responsible for peripheral and night vision and are sensitive to low light levels.

**Why Each Wrong Option is Incorrect**
**Option A:** Rods are not capable of colour vision, as they are sensitive to only one part of the visual spectrum and are not responsible for transmitting colour information to the brain.
**Option C:** The cortex is the part of the brain that processes visual information, but it does not play a direct role in colour vision. Colour vision occurs in the retina, specifically in the cone cells.
**Option D:** The optic disc is the point on the retina where the optic nerve exits the eye, and it is not involved in colour vision.

**Clinical Pearl / High-Yield Fact**
A common exam question trap is to confuse colour vision with peripheral vision. Remember that colour vision is mediated by cone cells, while peripheral vision is mediated by rod cells.

**✓ Correct Answer: B. Cones Cones are responsible for colour vision in humans.**