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.
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.)