Joel 2:31 reads: "The sun will be turned into darkness And the moon into blood Before the great and awesome day of the LORD comes" (NASB).
I see nothing in the Hebrew which would suggest another radically different translation like introducing "as" into the verse. Moreover, the LXX also reads:
METASTRAFHSETAI . . . hH SELHNH EIS hAIMA
Peter invokes Joel 2:31 in his discourse on Pentecost (see Acts 2:20). He also quotes the verse to the effect that the moon will be turned into blood. However, John seemingly alludes to Joel 2:31 in Revelation 6:12, yet he employs hWS ("as") rather than saying that the moon will become blood or turn into blood. Is he interpreting Joel 2:31 (under inspiration) or is there some other explanation for his use of hWS?
NET Bible: tn Grk “like blood,” understanding αἷμα (aima) as a blood-red color rather than actual blood (L&N 8.64).