https://food52.com/recipes/85869-best-blue-hawaiian-cocktail-recipe

“It might look strange that this drink uses both vodka and white rum, but there is good reason for it. Known for being flavorless and neutral, vodka is often derided by some (in my opinion, overly serious) drink makers, but it can serve a valuable purpose. In a drink like this, with so many intensely flavored ingredients, vodka can act as a “spacer,” providing room for the other ingredients to shine, while still maintaining the drink’s strength.”