Jeremiah 14:3
And their nobles have sent their little ones to the waters: they came to the pits, and found no water; they returned with their vessels empty; they were ashamed and confounded, and covered their heads. And their nobles have sent their little ones to the waters: they came to the pits, and found no water; they returned with their vessels empty; they were ashamed and confounded, and covered their heads.
Judah was mourning under a severe drought that had brought famine upon the land. In that distress even the servants dispatched by the nobles to draw water went to the pits and found none. They came back with empty vessels, ashamed and confounded, covering their heads in grief and disappointment. Such want and famine and mourning is what is signified by the black color of the prophetic black horse.