Biome Tinter is a client-side mod that lets you set the sky, fog, and lighting colours for every biome in your pack, with smooth fades as you cross the borders.
I made it because I wanted the biomes in my modpack to actually feel different from each other. Feel free to use it in yours too!
Every biome starts switched off, so installing it changes nothing until you decide what you want to tweak. As of 1.2.0, Biome Tinter ships with a built in atmosphere for 150 vanilla + modded biomes! Currently supported mods are: Biomes o Plenty, Incendium, Alex's Caves, Defiled Lands and Aether. You can add support yourself or you can suggest for it if you wish!

Join a world once and the mod writes config/biometinter/, one .toml per mod that adds biomes, plus a shared settings.toml.
Each biome looks like this:
["minecraft:desert"]
enabled = true
skyColor = "#CEB97C"
fogColor = "#E4CC97"
lightmapTint = "#F3EDDD"
Set enabled = true and give it a hex colour. Leave a field blank and that channel keeps its vanilla colour. Leave lightmapTint blank and it follows whatever the sky is doing, which is usually what you want.
settings.toml holds the global knobs:
enabled is the master switch, false turns everything off without touching your per-biome worktransitionTicks is how long a fade takes (60 by default, which is 3 seconds). Drop it to 10 while you are picking colours so you aren’t waiting between editsliveReload watches the folder and applies your edits without a restart (on by default)/biometinter edit opens the picker for the biome you are standing in and the sky updates as you drag, this is the easy way.
If you’d rather work in the files, open the toml in any text editor with the game still running, change a hex, save, and about a second later the sky fades to it.
Two things worth knowing:
/time set noon first, because the override backs off as the sun goes down and you will be chasing a moving target at duskIf your editor’s save doesn’t seem to land, run /biometinter reload. Some editors write through a temp file and rename it, which can slip past the watcher.
/biometinter edit opens the colour editor for the biome you are standing in/biometinter reload reloads the config from disk by hand (rarely needed, the configs update in real time as you save them)/biometinter status tells you what is actually loaded, entry count, fade length, and whether live reload is onAll three are client commands, so they need no permissions and work on servers that don’t have the mod.
Nothing besides this mod!
Colours only apply to the biome you are standing in. This is a tinting mod and not a shader, so don’t expect it to change how a distant biome looks from a mountaintop.
Performance cost is effectively zero. There is no world generation, no entities, no packets, and nothing registered into the game’s registries.