
Bubble-gum syrup is sugar syrup carrying the bubble-gum accord, a blend of esters that occur individually in real fruits and together in nothing.
Nothing reproduces it exactly, but the accord is not a mystery: strawberry syrup with a small measure of banana liqueur gets recognizably close, since isoamyl acetate carries the banana note in both. Failing that, a berry syrup makes a good drink that is no longer this one.
Bubble gum liqueur or vodka
Same flavor, plus alcohol, minus most of the sugar: both the strength and the sweetness need reworking before it stands in.
The pink and the blue bottles
In a finished drink they look nothing alike. The flavor does not always differ, since some makers color one syrup two ways. Read the label instead of the color.
The sugar concentration is high enough that nothing can live in it, and a sealed bottle sits in a cupboard for months. An opened one goes in the fridge, less for the syrup than for what the neck and the spoon carry into it.