Isaiah 50:3 - Matthew Poole's English Annotations on the Holy Bible

I clothe the heavens with blackness; or, I will or can clothe &c. What I once did in Egypt, when I drew black curtains before all the heavenly lights, and caused an unparalleled and amazing darkness for three days together, to the great terror of mine enemies, so I can and will do still when it is necessary to save my people. And therefore you have no reason to distrust me. I make sackcloth their covering; I cover them with thick and dark clouds, black as sackcloth, as is said, Revelation 6:12, or as that stuff of which the tents of Kedar were made, Song of Solomon 1:5. From this and some other expressions it appears that they wore a black sackcloth, which also was most suitable to the state of mourners, by whom it was used.