Place the fingerling and red potatoes in a saucepan; cover with water. Bring to a boil. Reduce heat; simmer 15 minutes or until tender. Drain; cool slightly. Transfer the potatoes to a large bowl.
Place the blue potatoes in a saucepan; cover with water. Bring to a boil. Reduce heat; simmer 10 minutes or until tender. Drain; cool slightly. Add the blue potatoes, egg, onion, parsley, dill, and chives; toss gently.
PREPARE THE VINAIGRETTE:
Whisk together the vinegar and remaining ingredients. Pour over the potato mixture; toss gently to combine. Serve warm, at room temperature, or chilled.
Notes
This recipe uses a trio of potatoes, but use all of one type if you prefer. Blue potatoes are starchier than the others and tend to bleed, so cook them separately. If you need to, prepare this dish a day ahead, but add the blue potatoes just before serving.
Be sure to cut potatoes to uniform size.
If you're preparing this recipe as GLUTEN-FREE- just make sure that the brand of Dijon you're using is GF.