Many thanks for the information, Jean.  I wasn't suggesting that "Black" and "Sailor's Life" were particularly related -as songs- (apart from shared floating verses in some versions), but that there seemed to be a close relationship between the melody Sharp found in Hot Springs, which, if I've understood properly, may be the source of your family's set, and the one Max Hunter got in Eureka Springs, both of which also show a strong connection to the tune Niles claimed for his own.  I'm still thinking that the "Sailor's Life" and "Died For Love" tune families might bear more examination for correspondences, but so far it's only a thought.  For what it's worth, and for anyone who might like to hear, here are some sound files:

DT: Black is the Colour (2)  (Lizzie Roberts, 1916)
Black, Black is the Color   -Short Real Audio sample of J.J. Niles.
DT: Black is the Color  No clear indication as to where this tune came from; it doesn't seem to be from Niles or Sharp.
Black is the Color  -Borrowed temporarily from the Max Hunter Collection (see above) and played at nearly double speed for (relative) ease of comparison.  The audio files on-site referred to above give a better picture, mind.
Died For Love  Noted by Percy Grainger, from Joseph Taylor of Lincolnshire.
There also seems to be some relationship to some of the Water Is Wide/ Waly Walytunes, but that's not so clear, and is certainly beyond my abilities to analyse.  Worth mentioning, just as a p.s., that another "Sailor's Life" variant at Max Hunter,  Sailor Boy  As sung by Mr. Harrison Burnett in Fayettville, Arkansas, June 15, 1959,also contains the lines

Oh [h]it's dark is th(e) color of my true love's hair
His cheeks is of a lily fair

Malcolm