- First: Yin-Yang comes from the Chinese. (Not THAT important, just something nice to know.)
There was a book (around 700 b.c. or even older I read) in which everything that happens (every phenomen) can be reduced to Yin and Yang constantly flowing into each other.
The Yang chakra wich is sealed in Naruto is the white side. Also put into connection with white, light, positive, sun(-rise), male principle in nature, energy, fire.
The Yin side stands in connection with female, negative, black, the moon, shaded orientation, matter, water. (And many more references but I chose the ones who connect / fit to the Naruto series.)
Obviously they are opposites. But: they can only exist with each other and they have a constantly changing balance. -> Is Naruto's actual chakra source from the Kyuubi incomplete, therefore there can be no balance and Naruto can't extend to his full power / Kyuubi's full power OR does Naruto just own all the "positive" chakra from the Kyuubi which got him to how he is now (he didn't let the hatred get control of him and stuff like this).
- There is a classic state: "Yin creates Yang and Yang activates Yin." Meaning that without day there can be no night. Without light there can be no shadows. Without winners there can be no losers. (Referring to Obito's statement here and the jutsu the Sage used to create the world.) Nothing can be totally Yin or totally Yang (therefore the two little circles of the opposite colour in each half) but there can be a imbalance. -> Why is Naruto not affected by some imbalance? Or is he and we don't know it (yet)? Is there even an imbalance if you just have the "positive side"?
- There exist some aspects in human medicine basing on Yin and Yang but I won't get deeper there. I will just state that Yang protects Yin. -> Naruto (positive side) protecting Sasuke (negative side) OR the positive aspects are stronger than all the negative ones? In my opinion Naruto could easily overcome the Yin chakra with his Yang chakra because he has a positive nature if he would become both / had both from the start.
- Yang is stated to be closer to heaven, Yin closer to earth. -> Reference to the Sage? (Known as creator of the Shinobi world = something like a god; god = said to be in heaven)
First of all, if you read everything stated above: THANK YOU. It took quite some time to look things up and put them together in a nice and Naruto connected way. ^_^
If anything I stated above is wrong please correct me (on a nice way). I will change it.