Jeremiah 14:5

Yea, the hind also calved in the field, and forsook it, because there was no grass.

Judah lay under drought and famine, with dearth spreading across the land and its people in want. In that distress the hind bore her young out in the field yet forsook it afterward, because no grass was to be found for food. Such a scene of utter destitution shows why black is the token of want and famine and mourning.