White shell on black.

Yin yang are not opposing forces (dualities), but complementary opposites that interact within a greater whole, as part of a dynamic system. Everything has both yin and yang aspects as light cannot exist without darkness and vice-versa, but either of these aspects may manifest more strongly in particular objects, and may ebb or flow over time. The concept of yin and yang is often symbolized by various forms of the Taijitu symbol, for which it is probably best known in western cultures.