Herbed tricolor pasta salad

1 1/2  c             plain yogurt
     3/4  c             mayonnaise
   1 1/2  tbsps         white wine vinegar -- or to taste
     3/4  c             minced fresh parsley
   1      lg            red onion -- quartered and sliced
     3/4  c             finely chopped fresh herbs -- basil, dill, etc.
   1 1/2  lbs           tricolor pasta

In a large bowl whisk together yogurt, mayonnaise, vinegar, parsley, onion and
herbs.  Cook pasta until tender, about 12 minutes.  Drain pasta and rinse with
cold water.  Drain and toss with dresssing and salt and pepper to taste.
Salad may be made 4 hours ahead and chilled, covered.  If pasta absorbs
dressing while standing, toss with about 3 tbsp warm water.