We disassemblied the picamera sensor, and found that, maybe there is an issue with the sensor itself. If you check the picture, I've taken about the sensor, you can see a dark circle in the middle of it:
The other strange thing is that, if we use the picamera without lens (so only the sensor), this circle color issue also exists on the pictures.
What do you think about this?
One more question: If I override the color shading table, it will also has an effect on the picamera preview or only on the captured pictures?
Thanks for your answer in advance!