As part of the the Pokémon All-Star event being held at Monaco Space, Seoul, South Korea, an alternate-colored Diancie will be distributed on August 13th, 2016 and August 14th, 2016 from 11:00am until 5:00pm on both days to players of
Pokémon Omega Ruby and Alpha Sapphire via infrared.
The alternate-colored Diancie is level 50 and know the moves: Diamond Storm, Moon Blast, Reflect and Return.
Sources:
http://pokemonkorea.co.kr/news/639,
https://story.kakao.com/ch/pokemonkorea/DNQUHZkHg00 and
http://pokemonkorea.co.kr/news/643