Jones says that yellow is one color that everyone has in their skin, it's just that some people have other colors in their skin as well. Nine out of ten times, everyone looks better with some yellow in their foundation. It will counteract unwanted tones (like redness) but enhance the tones that you do want to see.

(Nicole Kidman: cool,
Natalie Portman: warm)
To find out what undertones you have on your face, try this trick. In a well-lit area, wear a white shirt and stand against a white wall. Stare at your face in the mirror for about a minute. You should start to see colors: pinks, yellows, blues, oranges, etc. You may see different tones in different areas, such as pinks on the cheeks, blues under the eyes, yellows around the nose. If blues, purples, pinks and reds are what you see, then you have a cool-toned face. If yellows, oranges, and ochres are seen, then you have a warm-toned face.
Another way to determine whether you are warm or cool is the way you tan. If you tan easily, then you are warm. If you burn easily, then you are cool.
Happy findings.
