In my game UI, and if I view an atlas texture in the editor, in areas that should be transparent, now show a strange green background.
This happened when I upgraded to Unity 5.6.0f1.
I am using the latest version of NGUI - 3.11.2
I have tried regenerating the atlases using Atlas maker, and I've tried re-importing the textures, no difference.
You can see an image here...

Any ideas on how I can resolve this?
Thanks