Purple in WOSR usually brings my mind to P deficiency (either actual shortage of P in soil or inability of the roots to get it).
Wait until spring. You would be unlikely to see a margin over input costs from applying anything now. Your photo shows a crop most would be proud of.Where there is N overlap no deficiency showing but I agree it is most probably lack/unattainable P. Would a foliar application be worthwhile in November? Or wait to spring?