Joel 2:31

2:31 The sunlight will be turned to darkness

and the moon to the color of blood, ¹ 

before the day of the Lord comes –

that great and terrible day!

[2:31]  ¹ tn Heb “to blood,” but no doubt this is intended to indicate by metonymy the color of blood rather than the substance itself. The blood red color suggests a visual impression here – something that could be caused by fires, volcanic dust, sandstorms, or other atmospheric phenomena.