Creme de Violette is a low-proof, dark blue liqueur made from the flower, violet. The bottle I’m tasting is by The Bitter Truth. It’s actually “made from wild violet blossoms that grow in the Alps”, but some brands are made with artificial violet flavoring.
The Eagle isn’t one of the better-known cocktails. It uses raw egg, which is a little scary in this day and age to many people (and particularly to bars with lawyers), but you can use an egg substitute instead for safety. It also uses Creme de Violette, which no one’s thought of much in years,