Hi Jolana -- welcome to the Iris forums here at ATP!! We're always happy to see new members!!
It's true that Irises don't change colors. That's because each increase from the mother rhizome is actually a *clone* of the mother. There can be minor changes as a given bloom ages, but those changes should be consistent with each bloom.
Usually -- when Irises are said to change colors, what has happened is one of two things:
First -- another Iris has invaded the rhizome space of the Iris in question, and the rhizomes of the second Iris are dug up under the belief that they belong to the first Iris.
Second -- a bee pod was formed and the seeds self-sowed, creating an entirely different Iris that grows where the first one grows.
It is true that a given Iris grown in more than one location can have some color differences based on soil, weather and care, etc. But these disimilarities are generally not extravagant.
Hope this information is helpful to you.
Pictures can show a range of colors depending on the time of day they're taken, or variables within different cameras. Also, as some flowers age their color can fade. I just looked back and see I'm repeating what Arlyn said.. 
So.. I'll just say welcome again.
truer words were never spoken. I'll just leave it alone and continue enjoying it, no matter what color it is, 
