The most recent article from Women’s Wear Daily highlighting Gray Matter was in December of 2012. This article in particular claimed it would be a trend for fall 2013, and more specifically it would be luxury fabrics found primarily in suiting and it would be tailored. While this prediction was somewhat on point, it never really took hold like they thought in hindsight. Another interesting trend presented for spring 2014 by Style.com was the so-called “blue-period”. They believe that blue will have a moment in spring 2014 citing designers from Giorgio Armani to Calvin Klein Collection’s Italo Zucchelli using a full gradient of blue tones.

            Again, this is what I predict will be the natural progression from black-on-black to blue-on-blue to gray-on-gray. Every indication from Style.com to GQ to street wear photography indicates this will be the progression for the gray-on-gray trend.
Sources: http://www.wwd.com/menswear-news/fashion/mens-trend-gray-matter-6523186

http://www.style.com/trendsshopping/trendreport/071513_Menswear_Trends/