User blog comment:Xilinoc/Ch. 640 - BABY,HOLD YOUR HAND 3 (Mad Lullaby no.7)/@comment-1248963-20150827181112/@comment-1248963-20150828182034

Yes, absolutely, I forgot to mention it, but the miracle that keeps Bleach from being cancelled is its volume sales. Even if it's nowhere near where it was in its heyday, it's still one of Jump's bestsellers (as you mentioned, much better than Toriko, which WSJ pimped to be the next big thing when Bleach's popularity started falling). At this moment I think the only series that top Bleach in sales are One Piece, Assassination Classroom, and Haikyuu!!

I wasn't checking the ranking back when Kenpachi vs Gremmy took place, but I can take a wild guess that, being Kenpachi one of the most popular characters of the series, the chapters with the reveal of his zanpakuto have a good chance of having gotten a better ranking, which would explain having more color pages during that period.