Eosin is an acidic dye while methylene blue is a basic dye. When bacteria decompose lactose and produce acid, the bacterial surface carries positive charges and binds to negatively charged eosin, staining the colonies pink. In contrast, bacteria that generate alkaline metabolites carry negative charges and bind to positively charged methylene blue, forming blue colonies. A high level of acid production leads to dye crystallization and the formation of distinctive metallic luster on colonies. Dipotassium hydrogen phosphate maintains a stable buffering system to stabilize the pH environment during bacterial culture, and agar acts as the solidifying agent for the medium.