First, make a simple lemon syrup. Mix 1 cup water with half cup sugar and a pinch of salt, boil until it simmers and the sugar is all dissolved, then turn off and let this syrup cool completely.
Add blue coloring, and quarter cup of freshly squeezed lemon juice. Mix together and adjust until the color is to your satisfaction.
Now add equal amounts of this prepared blue lemon syrup and 7 up. Add ice-cubes or lemon slices and serve chilled! Enjoy!
TIP: Colour the water used for the ice-cubes blue to give a more vivid appearance, also used heart shaped ice cube molds for a cuter look