Thanks for the suggestion, Tom.
There's a couple of points I'd like to mention regarding this method:
First of all, this is not working for me. My scene just turns totally blue and dark with this method. Using Photoshop eye dropper on the same spot gives me a perfect white balanced image.
Second, why making things so complicated and counter intuitive by putting the automatic white balance function under a layer called "Tint" where we need to select the inverse of it? Why not just having a simple eye dropper tool under the White Balance layer? A simple white balance layer that include temperature and magenta-green options plus an eye dropper for automatic WB.
To make things even more complicated, all Corona eye droppers works totally different to any eye dropper out there! Instead of just clicking on the icon and then on the target, you need to hold click and drag. This usually leads to making mistakes not only because it's harder to move a mouse while holding click, but also because we expect the same behavior as any other eye dropper tool.
Seriously guys, why not addressing these kind of issues that would really make thigs easier for us? I know there are many new features to be added which are probably a priority. I've personally requested some of them. But to be honest, I'd rather choose to improve what we already have so at least our daily work using this amazing renderer was easier and more enjoyable.