**Core Concept**
The healing process of a contusion, or bruise, involves the breakdown and removal of damaged blood vessels and the repair of surrounding tissues. The color changes observed during this process are indicative of the different stages of healing.

**Why the Correct Answer is Right**
The green color of a healing contusion is due to the presence of **bile pigments**, specifically **bilirubin**, which is a breakdown product of hemoglobin. During the healing process, the body's macrophages and other cells break down the damaged red blood cells, releasing bilirubin into the surrounding tissues. The bilirubin is then converted to a green pigment, causing the characteristic green color of the healing contusion.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the healing process of a contusion.
**Option B:** This option is incorrect because it does not accurately describe the cause of the green color in a healing contusion.
**Option C:** This option is not relevant to the healing process of a contusion.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the color changes observed in a contusion can provide valuable information about the stage of healing and the extent of damage. A greenish color typically indicates that the healing process is progressing, but it's crucial to monitor the contusion for any signs of infection or delayed healing.

**Correct Answer: C. Bilirubin**