**Core Concept**
Red-green colour blindness, also known as dichromatic vision, is a genetic disorder affecting the retina's ability to perceive certain wavelengths of light. This condition arises due to mutations in genes encoding cone pigments, specifically the long-wavelength (L) and medium-wavelength (M) cones.

**Why the Correct Answer is Right**
The most common form of colour blindness is red-green colour blindness, which results from the absence or malfunction of the L-cone or M-cone photopigments. The L-cones are sensitive to longer wavelengths of light, typically in the red spectrum, while the M-cones respond to medium wavelengths, corresponding to the green spectrum. Individuals with red-green colour blindness often have difficulty distinguishing between these colours.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify a type of colour blindness.
* **Option B:** This option is incorrect because it is not a common type of colour blindness.
* **Option D:** This option is incorrect because it is not a recognized type of colour blindness.

**Clinical Pearl / High-Yield Fact**
Red-green colour blindness is an X-linked recessive disorder, predominantly affecting males, as they have only one X chromosome. Females, on the other hand, have two X chromosomes and are less likely to exhibit symptoms, unless they are homozygous for the mutated gene.

**Correct Answer: C. Red-green colour blindness.**