Now that you’ve determined your skin’s undertone, we must caution you: Using a foundation categorized as your respective 'cool' or 'warm' skin tone may not always be the most flattering choice. For instance, some foundations labeled cool-toned can end up making skin look overly pink, and those labeled warm can skew toward overly yellow. The goal is to select neutral foundation shades that have only the slightest hint of your skin’s undertone. You never want your foundation to be too pink or too yellow or too ashen.