On a Thanksgiving table loaded with heavy starches and creamy carbohydrates, a colorful, crunchy salad is a salve. A good one, with well-dressed fresh vegetables and seasonal fruit, illuminates everything around it while offering a welcome textural contrast. One bite of a smartly dressed salad can cut the richness of buttery potatoes and custardy or crisp stuffing, perk up gamy turkey meat and play off the dazzling tang of cranberry sauce.