To prepare dressing, in blender container combine herb vinegar, olive oil, vegetable oil, granulated sugar, paprika, salt, garlic, dry mustard, caraway seeds, and celery seeds. Blend until well emulsified.
Cut green beans on the diagonal in 1-1/2-inch pieces and cook in a large pot of boiling water until just tender-crisp. Refresh in cold water, drain and pat dry.
Cook the potatoes in a large pot of boiling water until just tender when pierced with aknife, 12-15 minutes. Drain and pat dry. Allow the potatoes to cool slightly. Slice potatoes into 1/4-inch thick slices, drizzling a small amount of dressing over potato slices and tossing to coat as you slice.
Add green beans to potato slices and toss to combine, drizzling a small amount of dressing to coat.
Dice red pepper, chop scallions and parsley, and add with remaining ingredients and toss to combine, drizzling just enough additional dressing to evenly coat salad. Grind black pepper over salad to taste and lightly toss again. Taste and adjust seasonings.
Salad is best if eaten the same day it is made - slightly warm or at room temperature - do not refrigerate! Leftovers should be refrigerated, but may be warmed slightly in the microwave before serving.
NOTE: I use Soleillou Radiant Wine Herb Vinegar which contains white wine vinegar, cloves, thyme, rosemary, fennel, bay laurel leaves, basil, and marjoram. This is available from Balducci's, New York City.
A reasonable substitute could probably be made by steeping these herbs in white wine vinegar for a few weeks before using.