I thought this was simple to understand.. I guess not.
Why is it then
Because I never understood either
It's because Naruto separated Kurama from it's chakra and KCM/BM consists of Yin Chakra,that and Kishi wanted Naruto to look unique and create a connection to the SO6P.
What about Minato? It's the yang part
He separated and sealed Kurama from the KCM/BM chakra.