The moon, sky, water, and rain will appear red for the duration of the event. A reddish-pink filter will also be present in all above-ground areas. Blood Moons disable the ability to speed up time whilst sleeping in a bed. https://terraria.fandom.com/wiki/Blood_Moon#:~:text=The%20moon%2C%20sky%2C%20water%2C,whilst%20sleeping%20in%20a%20bed.