Beautiful snake.

The dark area(purple/red) as you called it might be some kind of small hemorrhage.
It's not in the normal place you would find a pupil.
I've never seen a normal snake eye that wasn't curved and smooth.
Even a retained eye cap will still appear to be smooth.
It almost sounds like a deflated eye.
Some close up, clear photos would help.
Of course a visit to the Vet. might be best if you have a good reptile Vet. in your area.
I've had retained shed problems with many of my albinos, Checkereds in particular.
A little time in a shed box might be in order if you think it's a shed problem.
Hope some of this helps.
http://www.thamnophis.com/forum/husb...-shed-box.html