Stacked, uncorrected imageIt can be seen that the built in Chief ray angle correction has produced reversed vignetting, but also unacceptable chrominance effects with red predominating in the outer regions of the image.
The scope was pointed at a region of uniform sky and 50 flat-frame images were captured. These images were stacked in lxnstack to produce a master flat-frame.
Master flat-frameThe reversed vignetting and chrominance imbalance is very clear in the flat-frame
The image data were then stacked in lxnstack with flat-field correction.
Flat-field corrected imageIt can be seen that the flat-field correction made a good job of correcting for the pixel vignetting in the Raspberry Pi camera module when placed at the focus of the telescope.
Animation showing the effects of Flat=field correction
The conclusion is that whilst it may be best to use unsaturated data when observing and imaging the Moon, It should be possible to use flat-field corrected colour data for imaging the planets.