After reading this question about Chakra nature of Tailed Beasts. It came across my mind what is the relationship of the Yin-yang to the 5 Chakra nature elements? And how come you can classify a Chakra nature as Yin-Yang? Does it has something to do with the Chinese Zodiac or principles of Taoism?
For What is the relationship of the Yin-yang to the 5 Chakra nature elements?
Base from here:
Yin relates to one's spiritual energy and Yang relates to one's physical energy and it's necessary to utilise both of these in order to mould chakra for ninjutsu.
According to Yamato, the manipulation of Yin and Yang is the source of non-elemental techniques such as the Shadow Imitation Technique, Multi-Size Technique, medical ninjutsu, genjutsu, etc.
So in relation to 5 nature elements, I think it is the 6th type, having the techniques classified in this type as non-elemental techniques.
And about Does it has something to do with the Chinese Zodiac or principles of Taoism?
It is stated here that:
The concept of nature transformation parallels the real-life art, Onmyōdō (陰陽道; Literally meaning "The Way of Yin and Yang"), which is a mixture of natural sciences and occultism. It largely features Wu Xing and Yin and Yang.
Yin relates to one's spiritual energy and Yang relates to one's physical energy.
Mixing some yin and yang gives you chakra,
Chakra = Yin + Yang
Chakra is the resulting form of energy when two other forms of energy are mixed together. The two energies are referred to as "physical energy" and "spiritual energy". Physical energy is collected from the body's cells and can be increased through training, stimulants, and exercise. Spiritual energy is derived from the mind's consciousness (i.e. the soul) and can be increased through studying, meditation, and experience.
Chakra Control in 2 ways: Shape Control: Changes the shape of chakra
Nature Control: Changes the behavior, type and properties of the chakra.
Fire, Wind, Lightning, Earth and Water and there combos like Lava, Ice etc.
Other chakra types:
Tailed Beast Chakra, Senjutsu Chakra (Nature energy when Naruto in Sage mode) etc.