Dice the red potatoes into 1/2-inch cubes and place in a pot of cold water. Bring the potatoes to a simmer over high heat and cook until tender, about 10 minutes. Once the potatoes are tender, when pierced with a knife, drain and transfer to a large bowl.
To the bowl with the potatoes add the honey, mustards, oil and vinegar. Add the scallions, celery and dill, then toss everything with the honey mustard dressing. Season with salt and pepper and serve.