French translation: Coloration à l'huile rouge (Oil-Red-O)
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Explanation: I have recovered several documents off the web that have this term (a stain to reveal fat deposits in the body). Although I have not found a French document containing the word, I did find one in Dutch which uses the same term. At the same time, the Dutch writer DID choose to translate another staining product into Dutch - Sudan Black becomes Sudan Zwart - which would suggest that Oil Red O is a generic name, perhaps even a 'brand name' as such.
Incidentally, all the documents contained the title Oil Red O, Fat Red 7b. I don't know if you have it in your text as such. Maybe you inadvertently cut the phrase in the question, or maybe it is a specific strain of the stain...