cherry juice or cherry grenadine
Pour the grenadine into the bottom of your martini glass.
Pour the grapefruit juice over the back of a spoon into the martini glass, to create the second layer.
Pour the gin over the back of a spoon into the martini glass, to create the third layer.
Garnish the rim of the glass with a strawberry, cherry, or grapefruit slice.
These ratios are just recommendations, change up how much of each you put in the glass to get the flavor YOU enjoy.
If you like, rim the glass with colored sugar for extra flare!