The fresh, bright hues of the nasturtium blooms and chives will gradually fade over several hours, so this lightly-flavored vinaigrette will be most colorful if served shortly after being made. However, it will keep for 4 or 5 days in the refrigerator. In this case, bring it to room temperature (so the olive oil can become fluid again) before serving. Use over mesclun or any other greens you like. Add a few cherry tomatoes or some diced cucumber to your salad, if desired. Tip: Be sure to use an unseasoned (no salt, sugar or herbs added) rice vinegar. Tip: It is fine to use mostly leaves in the vinaigrette if you have only a few blooms and need to reserve them for the salad. The dressing just won’t be as colorful.