Are you using a ROM with support for RGB calibration? If so the selinux/contexts it may hold with the kcal sysfs path could prevent the app from using them. You can either pull all references to kcal out of the ramdisk, or use a root shell for now.
I'd also like to hear your results on pa_v2 control with N6.
# for Settings' access to DisplayColorCalibration
# Display color calibration
chown system system /sys/devices/platform/kcal_ctrl.0/kcal
chown system system /sys/devices/platform/kcal_ctrl.0/kcal_ctrl