This quoted text from the article sums it up pretty well:
Unlike previous magazines, the EPM uses a new, modified magazine body (and therefore not interchangeable, hence the different color) which presents the rounds at a more favorable angle to the rifle’s feedway, improving reliability and, importantly, preventing the hardened steel tips of new 5.56mm M855A1 Enhanced Performance Rounds from contacting the aluminum feed ramp section on M4 type rifles.
The new EPR mags have a tan body and blue follower, for those who don't wish to read the linked article.
Here is the TFB article link if you want to read the whole thing: http://www.thefirearmblog.com/blog/2016 ... es-rifles/