In a small saucepan, bring sugar, water and potatoes to a boil over high heat. Cook until potatoes are fork tender and simple syrup turns a deep purple, about 10 minutes. Let cool for 5 minutes before blending.
Place simple syrup and cooked potatoes in blender. Blend until smooth, about 30 to 60 seconds. Strain simple syrup into an airtight container and refrigerate until chilled, about 30 minutes. NOTE: Simple syrup can be stored in an airtight container for up to two weeks.
Fill cocktail shaker halfway with ice. Add tequila, lime juice, simple syrup and orange liqueur to cocktail shaker. Shake mixture until fully combined and well-chilled, about 15 seconds. Strain cocktail into chilled margarita glass or rocks glass ﬁlled halfway with ice. Garnish rim of glass with lime wedge. Stir in pineapple juice to change color and serve.
Use high quality filtered ice for an exceptional cocktail.
To rim glass with salt, run lime wedge around outer rim of glass and dip into kosher salt.
If you don't have orange liqueur, feel free to substitute triple sec.