Listen to the song here. The Foggy Mountain Boys was an American bluegrass band. The band was founded by guitarist Lester Flatt and banjo player Earl Scruggs. The group is considered one of the premier bluegrass groups in the history of the genre.
It probably means nothing. Yellow is the color we expect urine to be. If you take a vitamin supplement, these can sometimes give the urine an almost fluorescent color, a very bright yellow or yellow-green.
Also known as urochrome, urobilins are the pigment that gives urine its yellow color. Urine is usually pale yellow, but it can range from clear to a deep amber color in a healthy person. The level of yellow is determined by how hydrated a person is. A person who is very hydrated has more water to release through urinating, and thus has a lesser concentration of urobilin in their urine.