RealisticSeasons generates a biome folder with configuration files for every biome. You can change the colours of each season, the temperature modifier, if the biome should freeze in winter and if any plants should be changed.
Configuration for vanilla biomes
Here is the default FOREST.yml file:
## this file includes the following biomes: FOREST, WOODED_HILLS
Setting modify-plants to false will disable all changes to plants in this biome. Snow will also no longer be able to destroy grass and flowers.
freeze-in-winter includes the placement of snow and ice in winter. This also includes the removal of snow and ice after the winter ends. This should generally be false in snowy biomes since you don't want the snow and ice to be removed there. If you want the snow to be removed in snowy biomes outside of winter don't forget to also set keep-natural-snow to false in the config.yml.
show-snow-instead-of-rain changes if it should visually snow or not depending on the season. This does not include the placement of snow, it is purely visual. Only winter should be true in most biomes. All seasons should be true in snowy biomes though, you don't want it to visually rain there.
The colours of the seasons can be changed separately for each biome. You can almost create your own seasons. The config accepts all hex colour codes. The treecolor in autumn/fall should either be 1 colour or 5. Multiple tree colours are only accepted in autumn/fall to limit the number of custom biomes created by RealisticSeasons.
Configuration for custom biomes/generators
RealisticSeasons doesn't know exactly what to do with custom biomes supplied by world generators (datapacks, plugins). You can add extra biome configuration file(s) that will tell the plugin exactly what to do with them. If you do not create your own configuration files the plugin will just apply the same colour to all biomes. Snow in snowy biomes won't melt however and the plugin does automatically generate a correct temperature for the biome. The only exception is Terralith, RealisticSeasons has a build-in configuration for that generator with season effects fitting every biome.
Custom biome configuration files work exactly the same as vanilla biome configuration files. The file contains the same settings as the vanilla files, the only difference is that you're now able the change what biomes the file configures for. Here is an example custom biome configuration file:
You'll notice an extra line has appeared at the top:
This line tells RealisticSeasons for what biomes this file should configure. All the biomes on the list will get the season effects of this file. World generator(s) (plugins) often have a wiki with a list of the exact biome names and you can also find the name of a custom biome in F3.
You can create as many files as you want. Drop them into the RealisticSeasons biomes folder together with the vanilla biome files, the name does not matter.
Creating biome files for every custom biome in a world generator can be an insane amount of work. There is an easier option though. It is not as clean as creating configuration files for every biome since colours will be the same in everywhere, but it saves you a lot of time. Setting includes to ALL will make the configuration file configure for all custom biomes on your server. This is enabled by default. The plugin makes sure to not melt any snow in snowy biomes and it can also generate a fitting temperature for all custom biomes. A pretty good solution that instantly makes RealisticSeasons compatible with all world generators. Perfect if you just want to play with your friends but not recommended on a bigger public server.