The answer is: It became black as sackcloth of hair

Rev 6 vs 12

When the sixth seal is opened in Revelation 6:12, a remarkable and dramatic scene unfolds — the sun transforms into a deep, dark black, reminiscent of sackcloth made from goat's hair. This imagery is profoundly symbolic, reflecting not just physical darkness but a moody atmosphere of judgment and calamity. Sackcloth historically signified mourning; wearing it was often a public expression of grief or penance. So, when we envision the sun cloaked in sackcloth, it suggests a deep disruption in the natural order, a cosmic reaction indicating that something grave is unfolding.

Interestingly, this visual anticipates a motif found in other parts of Scripture. In the Old Testament, the concept of darkened celestial bodies appears often, especially around significant acts of divine intervention. Take, for example, Isaiah 13:10, where the sun’s lack of brightness foreshadows the coming devastation upon Babylon. This isn't just some surreal sci-fi imagery; the ancients expressed their understanding of spiritual events through their tangible experiences, often layering compelling poetic illustrations atop mundane realities.

As the story continues in Revelation, the sun's eerie darkness serves as a prelude to Apocalyptic upheaval and transformation — a strong vivid reminder of humanity’s sometimes reluctant relationships with profound change, loss, and rebirth. The tension captured in these verses invites contemplation about the nature of destruction and restoration, urging readers to explore deeper meanings hidden within the often cryptic symbology of Revelation.