In a large pitcher or punch bowl, whisk the thawed limeade concentrate with the cold water until no streaks remain.

Stir in the fresh lime juice, then taste: it should hit sharp and sweet at once, with no single note taking over.

Cover and refrigerate the base for at least 2 hours, so it is properly cold before the soda goes in.

Rub a lime wedge around the rim of each glass, then dip the rim in red sanding sugar and set the glasses upright to dry.

Just before serving, add the green food coloring if the shade needs help, then pour in the chilled soda and stir once, gently, so the fizz survives.

Pour over ice into the sugared glasses and drop a candy heart on top of each.