Final answer:
Vellus hair is the type of body hair that is not pigmented and rarely has a medulla. It is fine and colorless, helping in body temperature regulation and replaces fetal lanugo hair.
Step-by-step explanation:
The type of body hair that is not pigmented and almost never has a medulla is called vellus hair. This is fine, colorless hair that is present on most of the body. Vellus hair replaces the lanugo hair that covers the fetus and is shed close to birth. Unlike the more pigmented terminal hair that grows on the scalp, eyebrows, and eyelashes, vellus hair is lighter and serves primarily to help regulate body temperature.
The hair shaft of vellus hair consists of the cuticle and cortex, but it typically lacks the central core known as the medulla. The presence of medulla is more common in coarser hair types like terminal hair. Hair color is determined by melanin produced in the hair follicle, and since vellus hair does not have this pigmentation, it appears almost translucent.