You may use this mod in a modpack as long as you do not sell it via any means (Exclusive access from donations, etc.), you give credit (Linking back to this page), you do not make any changes to the mod aside from config files, and you follow all of the other terms listed in the license.
Serene Seasons is a Minecraft mod that adds seasons. Grass and foliage colors will change throughout the year, and in the winter, temperatures will shift and allow for snow to fall in some biomes that don't normally receive any. Seasons also affect various other features, like crop growth (Different crops are limited to different seasons), weather (More rain in Spring, more storms in Summer, etc.), and more!
Serene Seasons also works automatically with any biome mods, changing their grass and foliage colors without any additional tweaking required!