To make the Fruity Pebble-aperol, add 750 millileters to half a quarter container-full of Fruity Pebbles. Let the mixture sit for 15 to 20 minutes. Then, strain out the cereal with a cheesecloth. Set aside 1 1/4 ounces for this recipe and keep the rest for another cocktail.
To make the gum Arabic syrup, in a small sauce pan bring the water and sugar to a simmer. Add the gum Arabic and bring contents to a boil, stirring constantly. Cook for 50 minutes on high heat while stirring. Not all of the gum Arabic powder will dissolve, so strain the residual powder out. Cool and refrigerate. Reserve 1/2 ounce for this recipe and saving the rest.
To compose the cocktail, dry-shake all of the ingredients in a shaker (dry-shake = no ice). This technique emulsifies the contents and aerates the egg and cream.
Add an ounce of crushed ice or a single 1- by 1-inch ice cube to the shaker and shake until the ice melts. This may take up to 15 minutes (this is your arm workout).
Pour the contents into a Collins glass, then pour seltzer water into the glass up to the rim.
Place the glass in a blast chiller or freezer for 4 minutes.
Poke a hole in the center of the cocktail and pour more seltzer into it until the meringue rises (gently, to avoid overflow). Serve topped with Fruity Pebbles.