Marine animals often spawn in sync with some phase of the lunar cycle, and twilight’s color changes slightly around the time of the full moon, Sweeney says. Moonlight has a slight reddish tinge. So the waxing moon, which appears in the sky before the sun sets, shifts twilight a little toward the red. A full moon, however, just peeps over the horizon as the sun sets. As the moon wanes, it rises after sunset, leaving twilight bluer.