Purple Leaves On Leeks

My overwintered leeks were lulled into a false sense of security by the mild winter and then battered by the killer cold spell in February.
They seemed to be recovering and are still providing a useful take  for the kitchen.
I noticed today that the leaves are turning a bright purple.
Could this be a sign of a mineral deficiency - if so what do you recommend as an organic remedy? Or could it just be an indication they are coming to the end of their time?
appreciate your advice.
Many thanks in advance!

Thanks DD!
The leeks are still yielding useful stems for the kitchen.
I was concerned it was an indication of mineral deficiency.
Thanks again