mkay, so now it works. Something must have gone wrong on my Macbook air. Unplugged the USB cable and the power to the Atik a few times and it's now green.
very strange...
It actually turns out that you do need the power on for the Atik 314L on the Mac, if not powered up it won't be recognised and the light will still be yellow.
The QHY5 however has a faint red light at the back but still doesn't work.