one light bleaching (White leaves) to close to light to hot
two the plant naturally leaves dies turns yellow all part of life cycle
three you might have been giving to much n last cycles
four you got your feeding right.....!

i aslo grow similar trainwreck/blue also wheelchair/blue its all a matter of the plants life cycle some turn in 5th week some in 8th depends on room and strain, i also run whites that do purple/yellow in last 2weeks, but i trigger all things by environmental changes, but from what i can see they look fine as late in flowering it seems they are right on time to use up that n stored in the plant.