The tenses in the following description should be perfects and presents; the Authorized Version, by its inconsistency, destroys the unity of the picture. The gates thereof; i.e. the people assembled there.
They are black unto the ground. "To be black," in Hebrew, is "to be dressed in mourning" (so e.g. Psalms 35:14, "I bowed down in black"). Here we must understand the same verb which is expressed in the psalm, "They bowed down in mourning attire to the ground."
"Black," however, is not to be taken literally; it means rather "squalid, unwashed" (of garments).