Biome backgrounds

Biome backgrounds are images that appear behind objects and blocks in each biome. Each biome has its own set of backgrounds that usually show a landscape of the biome. In a world, each biome is randomly assigned a background from its own set, and can be changed by using a World Globe. Backgrounds can also be overridden using Monoliths. Backgrounds do not affect a biome in any way, except in The Hallow, where the current background affects the style of hallowed trees. Turning off backgrounds in Settings hides them, though ambient entities will still appear.

Jungle
Some Jungle backgrounds are combined with the current forest background.

The Hallow
Every Hallow background has a rainbow in it.

Glowing Mushroom biome
Glowing Mushroom backgrounds are combined with the current forest background.

Underground backgrounds
These backgrounds consist of only one layer, unlike surface backgrounds, and cannot be changed with World Globes.

Underworld backgrounds
Unlike the underground backgrounds, these have multiple layers like surface backgrounds do.

Trivia

 * The 3rd Hallow surface background features a large animated lake on its 3rd layer which cannot be easily seen in-game.