Unless you went to art school, you've probably never come into contact with a color wheel, but this simple device can make a big difference in your makeup-matching skills. Colors located directly opposite each other bring out the best in one another, while adjacent hues tend to clash. For example, blue and orange are situated across from each other on the wheel -- so blue-eyed girls can highlight their peepers using eye shadow in shades of orange and copper. Of course, this doesn't mean ladies with baby blues should head out and pick up a pot of bright orange shadow. Instead, look for blue or brown shadows with orange flecks or orange undertones for a more neutral way to make your eyes pop.