**Core Concept**
The yellow color of a bruise is due to the breakdown of hemoglobin in red blood cells, which is then converted to biliverdin and subsequently to bilirubin. This process is mediated by the enzyme heme oxygenase, which catalyzes the conversion of heme to biliverdin.

**Why the Correct Answer is Right**
Bilirubin is a yellow-green pigment that accumulates in the tissues as a result of heme degradation. It is further processed in the liver to become conjugated bilirubin, which is then excreted in the bile. The yellow color of a bruise is a result of the accumulation of bilirubin in the skin, where it is visible as a yellow discoloration. This process is a natural part of the healing process, as the body breaks down damaged red blood cells and replaces them with new ones.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the chemical process responsible for the yellow color of a bruise.
**Option B:** This option is incorrect because it is a type of porphyrin, which is a precursor to heme, but not the pigment responsible for the yellow color of a bruise.
**Option C:** This option is incorrect because it is a type of bilirubin, but the question is asking for the specific compound responsible for the yellow color of a bruise, which is bilirubin itself.

**Clinical Pearl / High-Yield Fact**
It's worth noting that the yellow color of a bruise can also be influenced by the presence of carotenoids, which are pigments found in foods such as carrots and sweet potatoes. These pigments can accumulate in the skin and contribute to a yellow or orange discoloration.

**Correct Answer:** C. Bilirubin.