Allotments 4 All

My leaves on my newly planted out cabbages[ in the last 10 days]  Hispi and Greyhound are going a bronzey colour, lower leaves at the beginning, but today the colour change seems to be creeping up.
Not sure whether to leave them or to give them a feed - but of what ?
The red Kalibos are not affected, but they were planted a bit earlier and the red kale planted at the same time do not appear to affected yet.
Any ideas greatfully received :)