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.
As with the yellow coloration of normal urine, red urine can range in intensity from a pink lemonade color (clear light pink) to that of tomato soup (active thick bleeding) to a deep opaque merlot color (liquefying clot). Hematuria, or blood in the urine, is likely the most common cause of red urine.