In a small nonreactive saucepan, combine the vinegar, sugar, salt, and peppercorns and simmer over medium-low heat, until dissolved, about 2 minutes.
Meanwhile, cook the radishes and peppers in boiling salted water for 2 minutes, until the radishes lose some of their color. Drain and place in a shallow dish. Pour the hot vinegar mixture over, let cool, and chill in the refrigerator for 15 minutes. These will keep, tightly covered in the refrigerator, for 3 days.