But in those days it was also a colour of paint that was jet black, similar to his mutt! Straight up, this was one of the other colours they did, see link below... Remember in those days the UK was not such a cosmopolitan population it is today and when the first black troops arrived from the USA they were treated as friends and equals, without any racial thoughts against them, as they should be, much to the chargrin of the white US troops who treated them poorly.
A Welsh View: 'Nigger Brown' Paint
Poor dog, if it knew the controversy he would spawn