Here is a short list of interesting facts on the yin yang symbol (referenced from Ancient History):
The concept of yin and yang represents duality and how opposing forces are interconnected.
Yin is feminine. Some Yin associations include water (transformation), the moon, the dark, earth, cold, and the spirit. Yin reaches its peak level of influence during the winter solstice. The tiger, phoenix, or the color orange also represent Yin energy.
Yang is masculine. Associations include fire (creativity), activity, the sun, warmth, mountains, odd numbers, and the underlying form of things. Yang's peak level of influence occurs during the summer solstice. Yang is also represented by the color blue and the dragon.