"革兰氏染色剂" can be translated as "Gram's stain" or "Gram staining reagent" in English.
"Gram's stain" is a commonly used term in microbiology to refer to the staining technique developed by Hans Christian Gram, as well as the reagent used in that technique.
"Gram staining reagent" explicitly refers to the chemical solution or mixture used for performing Gram staining.
Both expressions are acceptable, and the choice between them may depend on the specific context or preference.