Once you have selected a foundation color, there is only one way to be absolutely sure it is right for you: Apply the color all over your face and check it outside in the daylight. Check it from all angles and decide if it matches your skin exactly. If you applied it carefully but there are lines of demarcation at the jaw area; or if it looks too thick or too greasy, or gives the face an orange, pink, rose, or ashen tint; or if it looks heavy and opaque instead of sheer and light, wash it off and go back to the testers. In fact, you may need to test several types before you find the right foundation.
One practical guideline to narrow down your choices is to test many different colors at once. Begin with several that look like good possibilities and place stripes of each one in a row over the cheek area. The best choice is the one that blends almost perfectly with your skin color. The wrong choices will stand out, with obvious edges that don’t disappear into your skin. This technique is a reliable way to eliminate some choices, but I’ve also seen it go wrong more times than I can count because it doesn’t go far enough. Use it only as an elimination process; it does not replace the need to check out the color on your face in the daylight, nor the need to blend the foundation shade over a larger area of your face.
Keep trying on foundations until you find the best one. Once you’ve made a selection you feel good about, apply it all over your face, wait at least two hours, and check it again in the daylight. How a foundation wears during the day—does it change color or become too greasy or dry as the day passes?—can be evaluated only after you’ve worn it for awhile. Once you’ve assessed all these details, in the daylight, you can safely make a final determination as to whether this is the right color or type of foundation for you. Please take the time to follow this procedure. This advice will guide you in the right direction, and, ultimately, it is the only way to guarantee that you’ll find the right foundation. If you rely only on the salesperson and the lighting at the cosmetics counters, it will be pure luck if you end up with the right color. And if you get the foundation wrong, regardless of how perfectly you choose and apply everything else in your makeup wardrobe, those will all look wrong, too.