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.
As for as i searched with google.There are 3 versions of the Rinnegan:
original with tomoe, thus with "Sharingan" powers is the grey one
devolved tomoe-red Rinnegan that has not evolved fully.
Hybrid 6 tomoe - Sasuke's rinnegan. it's power is in between Kaguya's and Madara's rinnegan.
Sasuke Uchiha's left Sharingan became a Rinnegan when Hagoromo's spirit gave half of his chakra to Sasuke. His Rinnegan contains six tomoe split between its first two ripples and retains all of the abilities of his Mangekyō Sharingan. If Sasuke overuses the power of his Rinnegan, the tomoe will disappear until it has fully recharged, a process which takes a considerable amount of time. During this time, he is unable to use the Rinnegan's full power and apparently cannot even activate the Mangekyō in his other eye.
The power of the eye is based on the number of Tomoe inside , just like it was when comparing Sharingan.
The color of the Rinnegan is said indicate the current mode of the Rinnegan.
Only Red can cast the infinite Tsukuyomi
grey is to absorb jutsus and purple is to use them i think.
I'm not so sure of the color part .
Please correct me if i'm wrong. I'm also interested to know about this. Sorry for the bad English.