While it probably wasn't deliberate on the artist's part, the coloration of the cats as an inversion of Queen Beruthiel's in Tolkien's lore sort of reflects how Kayoko is guileless and kindhearted despite appearances.

"She had nine black cats and one white, her slaves, with whom she conversed, or read their memories, setting them to discover all the dark secrets of Gondor, so that she knew those things 'that men wish most to keep hidden', setting the white cat to spy upon the black, and tormenting them. No man in Gondor dared touch them; all were afraid of them, and cursed when they saw them pass"