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.
Urine consists of excess water and waste products that have been filtered from the blood by the kidneys. Its natural yellow color is due to excretion of urochrome, a pigment from blood. Depending on the amount of fluids you drink, your urine can range in color from almost clear (diluted) to dark orange (concentrated).