The author of The History of Galloway (1841) suggests Morrow or Murray is a corruption of Moor, “who from his swarthy complexion was called Black Morrow”. See The history of Galloway, from the earliest period to the present time by Mackenzie, William, of Galloway; Symson, Andrew, 1638-1712
“King James II of Scotland restored the lands when Sir Patrick’s son, Sir William, killed Black Morrow, a supposedly”Moorish” bandit living near Kirkcudbright. Sir William carried the head of the brigand to the king on the point of his sword. When King James demurred regarding the restoration of the estate, Sir William displayed the brigand’s head on his sword and advised the King to ‘Think on this’. This is the origin of the clan crest of this family and the Think Onmotto.” See Clan MacLellan
“James was somewhat astonished at the display, and was glad that the robbers had been disposed of, but forgot the promised reward whereupon Maclellan asked his Majesty to “Think on!” These words, with a Moor’s head transfixed on a sword, have since formed the motto and arms of the Maclellans. After the fall of the Douglases the family of Bombie acquired some of their possessions, and again became one of the most influential families in Galloway.” See KIRKCUDBRIGHT CASTLE AND THE LORDS KIRKCUDBRIGHT.