The Aviation is a classic gin-based cocktail that is shaken and served straight-up. It is basically a Gin Sour but with lemon juice sourness balanced by...
The violet liqueur matters. Where I live there are basically 2 choices for the violet liqueur - Bitter Truth Violet Liqueur and Rothman & Winters Creme de Violette. Bitter Truth makes a beautiful, clear, pale blue dink while R&W makes a muddy purplish gray cocktail. They taste different too - I prefer the Bitter Truth for taste as well as looks in this drink. Also, fine straining the lemon makes the drink more clear.