In an oversized Tom Collins glass filled with commercially produced ice (harder and colder than possible from ice machines or your freezer) pour:
1 oz gin
1 oz vodka
1 oz plain curaçao
1 oz blue curaçao
Fill reminder of glass with a sour press (if you don't know what that is fill with equal parts Tom Collins mix and club soda)
Stir well
Add a Maraschino cherry, sprig of mint and a long red straw. You'll have an inviting tall glass filled with a brilliant blue cocktail that will prompt your guests to inquire, "Is there any alcohol in this drink?" And after consuming two, drink a third and take a cab home. Despite being a bit complicated (not really, if you're behind a bar in San Francisco), this is a very refreshing adult beverage refreshment. Tastes great and great to look at.
When I can't locate blue curaçao I'll just make a pitcher of Grass Hoppers, using Half and Half.
Note: I began tending bar long before the invention of the Harvey Wall Banger and have equally old tastes in classic cocktails -- back in the day a Martini was always made with gin, Martini and Rossi vermouth, and garnished with two enormous pimento-stuffed olives. Oh, and we never had to pay income tax on tips, too.