Never seen that.......and changing to purple leaves look different
But iam pretty sure its no Defiency, plant looks fine.
Iam growing alot outdoors and on colder Nights the leaves start to turn purple,,,, but this way=? Nope,,,,
Its an open riddle for me
As long asthe leave lokks good and not looking dying... i wont be concerned,,, and i would ask the Fertiliser company ....