Originally Posted by BLOOD_GOD
He took on the "sage aura" because he had successfully obtained the Kyuubi's chakra in combination with the Sage's key and seal. Makes sense, doesn't it?
ok quick question.. do you think without the key and seal if naruto had taken on the fox xhakra that he would not have gotten the sage aura
simplified.. the seal and key is what caused the sage aura after getting the fox chakra