Foundation is important to match perfectly to your skin tone. The purpose of foundation is not to give you a tan but even out your skin tone. There are other products on the market geared to give a tan to your skin. I believe foundation should match your body.
It is harder to find a foundation without testing the shade on your skin. Whenever possible always test the foundation on your jaw line. Most people do not have a lot of redness in this area and is easier to see if the shade will match the body. Try to test three shades that you believe are closest to your skin tone and blend the shade into your skin. The shade that disappears is your perfect shade of foundation. If you are at a department store or can test foundation, I always asked for a sample. Sometimes artificial light can make a shade look perfect on your skin. However, when you are in natural light the foundation is darker or lighter than your skin tone. It is important to check the foundation in natural lighting to see the shade really matches your skin tone.
Never test foundation any wear except for your jaw line. Your body can be a different shade from your neck and face. You may end up with a foundation that is too dark or too light for your skin tone. You could end up with foundation demarcation lines, which means the foundation is the wrong shade.
I was recently testing foundation on my mother and the shade in the container seemed to be the perfect shade. When I put the shade on her jaw line the foundation was darker than her skin tone. (I was in natural lighting) It was not the correct shade and I needed a lighter shade. The shade in the bottle seemed to be too light for my mother but it turned out to be the perfect shade.
Sometimes people can have different tones in her skin. The outer portion of their skin is darker and the middle part is lighter (or it could be the opposite). It can be difficult to find a foundation. One way to counteract the different tones in the skin is to use to different shades of foundation. One shade should be for the darker parts of your face and another shade of the lighter portion of the face. However, foundation can be expensive and not everyone can afford to buy two foundations. Another option is to find a foundation in between your darker parts of the face and lighter parts of the face. This way you can create one shade all over your face when the foundation is blended into your skin.
Foundation should always be the same shade as your skin tone. It is important to match the foundation color to your body. Foundation should look like your skin and not create a different shade.