## Core Concept
Pseudomonas aeruginosa is a gram-negative bacterium known for producing various pigments. These pigments play a significant role in its identification and are associated with its pathogenicity. The most notable pigments produced by P. aeruginosa include pyocyanin, pyoverdine (also known as fluorescein), and pyorubin.

## Why the Correct Answer is Right
Pyocyanin is a blue-green pigment produced by Pseudomonas aeruginosa. It is one of the key virulence factors and pigments that help in the identification of this bacterium. Pyocyanin is responsible for the characteristic blue-green color of the colonies and pus in infections caused by P. aeruginosa. This pigment has also been implicated in the pathogenicity of the bacterium, as it can generate reactive oxygen species.

## Why Each Wrong Option is Incorrect
**Option A:** Pyoverdine (or fluorescein) is a fluorescent pigment produced by P. aeruginosa but is not exclusive to this bacterium as it can also be produced by other Pseudomonas species.

**Option B:** Pyorubin is not a commonly recognized pigment associated exclusively with P. aeruginosa.

**Option C:** This option is not provided, but based on common pigments, we can infer that other pigments might not be exclusively produced by P. aeruginosa.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that the blue-green color of pus or wound discharge can be a diagnostic clue for P. aeruginosa infection, largely due to the production of pyocyanin. This is particularly relevant in patients with cystic fibrosis or those with compromised immune systems.

## Correct Answer: D. Pyocyanin.