Crème Yvette is a proprietary liqueur based on a crème de violette, including raspberry, blackberry, cassis, strawberry, honey, orange peel, and vanilla notes.
Production of Crème Yvette stopped in 1969, but was restarted in 2009 by Cooper Spirits, the producer of St. Germain elderflower liqueur.
Crème de violette is an acceptable substitute but it is not exactly identical.