Board Thread:Naruto Gaiden/@comment-24949460-20150704110328/@comment-734582-20150704162138

Nano555 wrote: Where is the Truth-Seeking Ball, and the coat with the typical markings of the Six Paths Senjutsu.The Rinnegan above nine magatama, on its back. As others have pointed out, the Truthseeking balls were all destroyed. I don't agree with the idea but it's unfortunately canon.

As i mentioned, it's likely that Hagoromo's chakra is gone, which probably was what caused the markings you described. Hagoromo did have the Juubi in him for a long time and so his chakra likely contains Juubi chakra hence the markings.

it explains why Naruto can use Kurama Sage Mode without pigmentation. The Sage's chakra is gone which is why the look defaults to Kurama Cloak but lacks the traditional fiery nature. It explains why his cloak is coated in Kurama chakra yet he seems to have a 6PSM-like dark underarmor.