Peel and chop the russet, sweet, and red potatoes into bite-sized pieces.

Place the potatoes in a large pot, cover with water, and bring to a boil.

Boil for 15-20 minutes or until the potatoes are tender.

Drain the potatoes and refrigerate until completely cooled to maintain their texture.

In a mixing bowl, whisk together the mayonnaise, chopped onion, sugar, and vinegar.

Add the cooled potatoes to the bowl and stir gently until well combined.

Season with salt and pepper to taste.

Serve immediately or refrigerate for a few hours to allow the flavors to blend.