1. Why his hair turned white, he looks like a Zetsu...
2. And how he sealed the juubi inside him?
1) Rinne Tensei as stated or side effect of being the Juubi Jinchurriki
2) I'd go with Izanagi. When Obito explains the power to Konan, he says it was the jutsu the Sage used to "create", then explains its power as "turning imagination into reality." Obito used it to create this reality where he is the Juubi Jinchurriki.
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1. Why his hair turned white, he looks like a Zetsu...
2. And how he sealed the juubi inside him?
That Izanagi theory it's actually very plausible, can Izanagi have that range of power, it's the question that comes in my mind...