1. On June 4th, Riot changed the matchmaking algorithm to make the purple team to have higher MMR. As a result blue side win rate dropped from 55% to 52%.
2. But, as a side effect, challenger players now play on the purple side 58% of time (it used to be 50% prior to June 4th). Top challenger players (i.e. top 10) play on purple side close to 70% of the time.
[Check out my blog link for data, charts, and some analysis.](http://sufficientblogging.blogspot.ca/2014/07/riot-changed-matchmaking-algorithm-to.html)