Pokémon GO will be celebrating Halloween from October 26th to November 1st, as trainers enjoy an increase in candy and in spooky apparitions.
Niantic Inc. also mentioned that having a Pokémon buddy active will give you four times the usual rewards, catching a Pokémon will give you 6 candies and transferring will give you 2 candies.
There was also an update last night, and it included a feature where the eggs will be colored based on distance needed to hatch them:
Source: Pokémon GO / Youtube