*Foundation should not change the color of your face, remember this rule!*
Your foundation should appear invisible. What do I mean by that? Your ideal foundation shade should sink into your skin color, and disappear. Only then can you be sure you have found your exact match.
How do you pick the right shade? Always match your foundation color by applying it to the side of your face near your jaw/lower cheek area. Not the inside of your wrist and not on the back of your hand.
Apply it directly onto your face and look at the color in natural daylight. If that means walking out of the store to do so, then do it. Trust me, it is worth the effort. There is nothing worse than badly matched foundation and that horrid demarcation line around the face.
If you are COOL, stick with foundations that have a pink undertone. Stay away from anything that looks orange or peach in tone.
If you are WARM, look for a foundation that has a golden or yellow undertone. Stay away from pink, you will look ashen.
If you are NEUTRAL, you need a variation of either tone, depending on the season and your current shade.