I noticed the same thing on my porcelains, was very excited to see so much purple and I even thought I might tell one variety from the other that way.. but after drying down a few more weeks the outer purple wrappers also turned white.
It's one of those things about the whole garlic process, you had to be there to smell the Spanish Roja when it was pulled, or to see the rainbow colors on New York white, or to admire all the purple on Music when it was first cleaned up....
Secret beauties we growers enjoy, the buyer may never know...