I've got Kali 4.16.0 installed on an Early 2013 13" Macbook Pro. When I'm booted into GNOME, I can change the screen brightness and it shows the UI pop-up shwoing the brightness level, however if I try to change the keyboard backlight level I also get the UI pop-up but the level does not change.

I can use
echo 0 > /sys/class/leds/smc::kbd_backlight/brightness
to change the backlight brightness.