Combine the blue raspberry syrup and pineapple juice in a pitcher and stir until the color turns an even, solid blue with no streaks of syrup left.

Cover and chill the mixture for 20 minutes.

If using sanding sugar, wet the rim of each glass with a lemon wedge and dip it into a shallow plate of blue sanding sugar.

Fill each glass with ice.

Stir the chilled syrup mixture once, then top the pitcher with the lemon-lime soda, pouring slowly down the side.

Give the pitcher one gentle stir to combine, then pour immediately over the ice.

Garnish each glass with a lemon wheel balanced on the rim.