2. Second assumptions -
Naruto : October : Autumn
Sasuke : July : Summer
- where Autumn is yin and Summer is yang*:
Taken from the new opening theme of Naruto Shippuuden. One can look at Naruto and Sasuke as yin and yang respectively by imagining their heads = the perforated end of a half yin/yang and their feet = tail of a half yin/yang.
*Note that the appropriate colors are reversed however - darker tones (yin) for Neji/Sasuke and brighter tones (yang) for Hinata/Naruto. A brief speculation for this is mentioned in the First Theory - Yin Yang (