Contrast- the element that permits one item to stand out clearly from others.

Contrast is important in good design because it gives emphasis and avoids uniformity.  With this element you can provide strong contrast which makes for a youthful and busy look, and a contrast that is weak will appear more conservative. By treating items differently from one another you achieve contrast.  Contrast can be abrupt or subtle.  Robin Williams, a graphic designer from my home state of California, talks about contrast as well as several other elements in her book Non-Designer Design Book.  Williams book talks about the principles for the visual novice (beginner).  She has written other books, as well as design columns and articles that contribute greatly to the graphic design field.