**Core Concept**
The ureter is a paired, muscular tube that connects the kidney to the bladder, playing a crucial role in the urinary system. Identifying the ureter during surgery requires a clear understanding of its anatomical location and characteristics.

**Why the Correct Answer is Right**
The ureter is typically identified by its peristaltic movements, which can be observed during surgery. This is due to the presence of smooth muscle cells in the ureteral wall, allowing for peristalsis and the propulsive movement of urine from the kidney to the bladder. The ureteral branches of the renal and iliac arteries and veins also provide a distinctive landmark for its identification.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the ureter is not typically identified by its color, as it blends in with the surrounding tissues.
* **Option B:** This option is incorrect because the ureter is not usually identified by its size, as it is a relatively small structure compared to other abdominal organs.
* **Option C:** This option is incorrect because the ureter is not identified by its location in relation to the psoas muscle, as it is a more specific and indirect landmark.

**Clinical Pearl / High-Yield Fact**
During surgery, observing the ureter's peristaltic movements can help identify its location and prevent damage to this critical structure.

**Correct Answer:** C.