For this calibration, use a scene with flesh tones. The scene I used in "Life is Beautiful" featured relative close-ups of two people, with green plants behind them. Focus on the faces of your selection and watch for subtle changes towards red or towards a more washed-out color. Play in that range until you find the most natural-looking flesh tones. Keep an eye on other signals like plants or flowers in the background. All elements should remain looking very life-like.