A common theme in the show are the colors black and white.

One of the first mentions of these colors, is when Locke is playing Backgammon in "Pilot - Part 2". Walt comes over and asks him about it. While holding up black and white playing pieces, Locke tells Walt, "two players, two sides, one is light, one is dark."

Later on, in "House of the Rising Sun", when Jack and Kate find the cave people, we see the colors again. On one of the bodies, Jack removes a small bag that contains a white stone and a black stone. When Locke shows up, Jack quickly hides the stones.

The colors, of course, my also represent:

• Black: evil, hate, darkness
• White: love, happiness, good

Where We Have Seen This:

• In the backgammon game throughout season 1.
• In Claire's dream in the episode "Raised by Another", Locke appears in the dream with one eye white, the other black.
• The two bodies in the caves are holding a small bag, containing two small black and white stones.
• Sawyer's new glasses are made from two seperate pairs. One of them was black, the other was white.
• When we have seen the monster, we see black smoke, Locke claims to have seen a bright light (possibly white?)
• The Dharma logos are made of black and white symbols.

Yin Yang
Yin and Yang are two principles in Chinese philosophy and religion: yin represents a dark, passive, feminine figure, and yang symbolizes a light, active, masculine figure. Together they are believed to influence the destinies of other people and things. (Google Definitions)

The Dharma Logos:
The black and white Dharma logos greatly resemble this symbol used in the I-Ching and Feng Shui. It is called the Ba-Gau. It is traditionally represented in the shape of an octagon. Each facet of the octagon is assigned at least one of life's aspects, such as career concerns, a natural element, and at least one color. Feng Shui has been practiced for 4,000 years.
Other links about this:

• http://www.buy-utah.com/feng_shui.htm
• http://webpages.charter.net/fengshui/bagua.htm
• http://www.flc.losrios.edu/~willson/fitns414/handouts/trigrams.html
• http://www.windwatrcanada.com/whatisfs.htm