1. If precise color description is a consistent part of your narrative and prose style (and not simply a flagging device for the characters you wish to squee over or shudder at.)
2. If you are seeking to insinuate that the item in question is, in fact, made of or stained with dried blood (as in Charles Dickens's short story "Captain Murderer".)
One wrong reason? Using such a comparison as a scare chord, as an automatic tag that the character possessing the deep red attribute is EEEVILLLL. That's not only lazy writing but an implicit insult to any number of perfectly nice people who happen to like Chanel's "Vamp" nail polish.
(The Kushiel Saga had the heroine wearing a cloak of a specific blackish-red termed sangoire, reserved for those of her rare and cherished neurotype--a Special Snowflake Symptom, perhaps, but it averts the above cliche.)
(A tip of the red cap to kosaginolegion's grumbles about Mercedes Lackey and Lois Lowry.)