Pink Moon
The Moon does not turn pink, and the name has never claimed it did. It is named for Phlox subulata — moss pink, or creeping phlox — one of the earliest wildflowers to carpet ground in eastern North America. Every April a fresh wave of people go outside expecting a coloured moon and see an ordinary white one, which makes this the most reliably disappointing name of the twelve.
Where the name comes from
It is also the one with the most religious weight attached: the April full moon is usually the Paschal Moon, which sets the date of Easter, and through that the date of Passover is entangled with it too. That part of the calendar is far better documented than the flower.
Also called Sprouting Grass Moon, Egg Moon, Paschal Moon.
Old Farmer's Almanac; the Paschal computation from the ecclesiastical calendar