All biomes have Serene Seasons tags made accordingly to their appearence. If the biome is already colored brightly or it's an icy biome- it is blacklisted/ added to "slight seasonal color change" list in order to remain close to how it's supposed to be when created. Every other biome changes colors as usual.

If you don't like it this way-you can change biome tags inside the mod's .jar. Open the .jar with 7zip or another tool and go to "data/sereneseasons/tags/worldgen/biome/...". Here there are 3 files (open with Notepad):

blacklisted_biomes: no seasonal changes at all. Default: Ice Wasteland, Snowy Hills, Aelven Woods and Mossy Swampland

lesser_color_changed_biomes: lesser changes, but  they still change colors and can have snowfall in winter. Default: Autumnal Grove, Crimson Wood, Elder Forest, Fairy Forest, Fir Woods, Golden Aspen Forest, Grim Forest, Old Swamp, Prairie, Redwood forest, Snowy Forest, Snowy Coniferous Forest and Tundra.

tropical_biomes: all hot biomes

Most of the trees have non-decaying leaves due to their handmade and complex structure Vines on some trees are not rotated properly, that's the Oh The Trees You'll Grow issue. Unfortunately, it's not fixed yet, but Corgi_Taco is aware of it, so I hope it will be fixed.

As it is a datapack in core, you may experience some incompatibilities with other datapacks/mods, that change the same things, like vanilla biomes, using the datapack system. But mostly it should be comaptible.

As a datapack in core, this will most likely ruin the world if you delete it or change something inside it's .jar. Be very cautious and create backups of your important worlds!