The change in color tone of crude drugs during storage of decoctions is one of the factors leading to poor drug compliance of decoctions. We experienced a case of a decoction including Aluminum Silicate Hydrate with Silicon Dioxide (Kasseki) turned into bright blue color after it was combined with goreisan. We therefore examined to find out possible causative crude drugs using an airtight container and performed a component analysis by the TLC. As a result, we found the following: Kasseki under the coexistence of Cinnamon Bark (C. Bark) and Atractylodes Rhizome (A. Rhizome) turned into a bright blue color in several hours. In this coloration, aluminum silicate hydrate, cinnamaldehyde and atractylon, which derive from these 3 crude drugs, were involved. This coloration change of Kasseki under coexistence of C. Bark and A. Rhizome was a vivid and sharp reaction generated in several hours. From the perspective of maintaining medication compliance, it is important to provide a full explanation to patients about the change in coloration of Kasseki, when decocting crude drugs that contain C. Bark, A. Rhizome, and Kasseki. To avoid coloration, it is considered useful to put Kasseki in a separate sachet, isolated from other crude drugs in storage, and to mix in Kasseki just before decocting.