If you are using a bright colored eye shadow, or one that is much darker than your skin as the color in the crease of your eye, you may want to use a blending shadow to give a more, well, blended look. What I mean by this is to take a color close to your skin tone, but a half shade darker and apply it just at the outer edges of the shadow you applied in your crease. For fair skin I recommend (these are all MAC shades) Wedge or Omega, medium skin tones can use Soba and for darker skin use Cork. Apply the color with a very light hand and use a blending brush, such as the #217 from MAC, then apply your highlight color under the arch of your eyebrow. Go ahead and give it a try.