No, it will NOT turn purple. But freezing is an excellent method to preserve your stash.
Friend of mine always keeps it in the freezer and everytime I come over and smoke it, it's always some of the strongest weed I've ever smoked.
He also has a big bag of ice and I came up with the idea to hide the stash under the bag of ice which keeps it even colder.
Until I have my own apartment, I would put weed in the freezer.