Fill a large, heavy pot with water and bring to a roiling boil. Add the cranberry beans and cook for 10 minutes. Add the green and yellow beans and cook for an additional 10 minutes, or until all beans are tender. Drain.

Combine the beans with the tomatoes, red onion, 1 tablespoon minced marjoram, and feta cheese in a large bowl. Toss well using a large metal spoon. Dress with the dressing (recipe below), and toss again. Serve at room temperature with a flourish of extra marjoram.

Whisk together the lemon juice, mustard, salt and pepper until the salt is dissolved into the juice. Gradually whisk in the olive oil.