Are you talking about B12 added to compound vials? If so check the compound subreddit. Otherwise search results say vitamin B12 is a red crystalline powder and the only vitamin with cobalt. Injections are red or reddish-pink because of cyanocobalamin or hydroxocobalamin.
Quick question. A lot of places sell B12 already as a red liquid in vials so it must be mixed with something. Does anyone know what liquid they use and what the shelf life is after opening?