I am recording from 8 raspicams using picamera. Initially the cameras gives the desired output but soon there is purple band/haze which appears on 3 cameras out of 8.
I checked for digital_gain, analog_gain, brightness, contrast, sharpness values through all 8 cameras for each frame and it was consistent across all 8 cameras and all frames in each frame for 1 hr recordings.
One more thing, I am driving these outputs to zmodo multi channel system to check the video output and Zmodo uses PAL scheme.
Here are sample of initial setup frame and post purple haze addition, Trust me the haze is more than the one shown in the image.