User blog comment:Xilinoc/Ch. 553 - Frozen Cross/@comment-1351982-20131016161206/@comment-11051098-20131016230936

Urahara said that the pills he made, upon contact with the captain's body, would cause the Bankai to hollowfy, turning it into "poison" for the Quincy. I think Daigured Hyôrinmaru has just taken on a slightly hollowfied appearance because of the pill, taking the effect the pill was designed to give.