What is "the moon runs down in a purple stream" referring to? Regarding this verse of the traditional folk song “Didn’t My Lord Deliver Daniel”:

The moon runs down in a purple stream
And the sun refused to shine
And every star did disappear
Yes, freedom shall be mine


I realize that the second and third line allude to the Biblical passage about the sun disappearing at the moment of Christ's death. But what about the first line? What is this an allusion to?
In Joel 2:31 NIV, which says that 


  The sun will be turned to darkness and the moon to blood before the coming of the great and awesome day of the LORD.


as well as in Mark 13:24-25 NIV


  However, after the tribulation of those days, ‘The sun will be darkened, and the moon will not give its light, the stars will fall from the sky, and the powers of the heavens will be shaken.’


These verses contain the most probable meaning of the verses, especially considering the different fourth line on this website. Seeing that the last line in that version is "King Jesus will be mine", the lines most directly refer to the coming of the Son of Man and the events preceding it. So the second and third lines do not allude to the death of Christ, but rather, the second coming of Christ.   

As for the 1st line, "The moon runs down in a purple stream", it refers to two things. First would be the "purple" color referencing the royalty of "Jesus" in the version above. Second would be the "runs down" refers to the moon turning to blood in Joel 2:31, afterward not giving its light as in Mark:13:24-25.