The ELISA (enzyme-linked immunosorbent assay) is a test which uses color change and antibodies to identify a substance. An indirect ELISA is one of three ELISA tests.
Urine varies in appearance, depending principally upon a body's level of hydration, as well as other factors. Normal urine is a transparent solution ranging from colorless to amber but is usually a pale yellow. In the urine of a healthy individual the color comes primarily from the presence of urobilin.
The most common color of urine is yellow, which is caused by the presence of urobilin, a biochemical waste product generated from the breakdown of old red blood cells. (Your body makes about 2 million new red blood cells every day, and recycles an equal number of old ones.)