You can protect regions in your world from season effects using WorldGuard. Very useful if you have a spawn area for example and you don't want any season effects there that might mess up your spawn. RealisticSeasons adds the following flags:
Settings this flag to false in a region will completely disable all season effects there. No colours, no block changes, no mob spawning, a locked temperature at 25°C.
Setting this flag to false will only disable block changes. This means no ice and snow will be placed and plants won't be changed. Colours will still be there and so will the animals.
Setting this to false will only disable season mob and animal spawns.
Permanently change the season in the region. The flag will override the normal season. The changes are only visual, block and mob changes of normal seasons do not apply. Accepted values are WINTER, SPRING, SUMMER and FALL.
Permanently set the temperature in a region. It will completely override the normal temperature and it can be any number.
All players in the region will get their temperature reduced/increased by the value specified.