What it is
An appearance sets a biome's colours and fog. It never changes the terrain or the blocks, only how they look.
Made by6
Used by8
Good to know
Blank means inherit
Leave a colour blank to keep the one underneath. Overlay Appearances only replaces the colours its top layer sets.
Resolution
Minecraft stores biome looks in 4 by 4 by 4 cells, so appearance changes are never sharper than that.