**Core Concept**
Postmortem staining, also known as livor mortis, is a discoloration of the skin and underlying tissues that occurs after death due to the pooling of blood in dependent areas. This phenomenon is influenced by the gravitational forces acting on the body and is a result of the breakdown of cellular integrity, leading to the release of hemoglobin into the surrounding tissues.

**Why the Correct Answer is Right**
The correct answer is related to the breakdown of hemoglobin and the release of its components, such as biliverdin and bilirubin, which are responsible for the greenish or yellowish discoloration seen in postmortem staining. However, in the case of a red-brown color, it is likely due to the presence of methemoglobin, a form of hemoglobin that is oxidized and unable to bind oxygen. Methemoglobin is formed when hemoglobin is exposed to certain substances, such as nitrates or nitrites, which are commonly found in the environment.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specifically relate to the red-brown coloration seen in postmortem staining. While hemoglobin is indeed involved in the process, the specific form of hemoglobin responsible for the red-brown color is methemoglobin.
**Option B:** This option is incorrect because it is not directly related to the postmortem staining phenomenon. While certain conditions may cause a similar discoloration, it is not the primary cause of the red-brown color seen in postmortem staining.
**Option C:** This option is incorrect because it is not a specific cause of the red-brown coloration seen in postmortem staining. While certain substances may contribute to the breakdown of hemoglobin, they are not the primary cause of the red-brown color.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the color of postmortem staining can vary depending on the circumstances surrounding the death, including the presence of certain substances or conditions that may affect the breakdown of hemoglobin. A deep red-brown color may indicate the presence of methemoglobin, which can be a useful clue in forensic investigations.

**Correct Answer:** C.