Well in chapter 602 Madara implies he gave the Rinnegan to Nagato. If that turns out to be true then the following problem arises. Since we already know that Madara awakened his Rinnegan after he already had awakened his eternal Mangekyo Sharingan then shouldn't Nagato have the Sharingan ability too? Remember Kakashi. He just got his Sharingan transplanted and could already use it.No awakening no nothing. So if Nagato had Madara's eyes then why didn't he have sharingan powers too?