Is the Rinnegan completely purple in Naruto? This is probably a really stupid question, but is the Rinnegan completely purple from the front to back, or is it just the iris that's purple? Pictures would help.
In this link there is one statement :


  The Rinnegan is characterised by a ripple pattern that spreads over
  the eyeball.


Since it spreads over the eyeball then in conclusion we can say that it is completely spread from front to back as it covers the whole eyeball.

Also there is no evidence which proves that Rinnegan purple color is limited to that pupil area only.