For vinaigrette whisk together orange juice, marmalade, oil, vinegar, garlic, salt and peper until blended. Chill 1/4 cup of vinaigrette. Toss remaining vinaigrette over radicchio. Let stand 15 minutes; drain.
Grill radicchio, cover with grill lid, over med-high heat 1 minute on each side or until crisp-tender. Toss with reserved chilled vinaigrette and serve immediatley.