Hi Paul,

I think that you are viewing your flats in the fits viewer in a stretched and automatically debayered form. If you open up "configure KStars" and open the "fits viewer" tab. There are a number of options. It is likely that you have auto debayer ticked. Uncheck this and you should be able to view the flats in mono, just auto stretched. This will give a better idea of what they look like. Remember that the flats are never used in a debayered form so the red cast is irrelevant. Just stacked into a master in undebayered form. Your vignetting will be dealt with in the calibration of the lights with the flats (and darks).
The fits viewer just views the images but does not change them so you don't need to worry that there is a problem. You can still use the flats that you have taken. I have never examined any of my images using the autodebayer in fits viewer as I find that it is not as helpful as a mono image in determining contrast and exposure.
All my final calibrated and integrated lights have a prominent red cast but this can be dealt with in histogram transformation. As I said, a quick way of fixing this in the final image is doing an autostretch using unlinked RGB channels. This largely removes much of the redness.
You may be able to attract more help in relation to the use of APP with this camera if you were to start a new thread with the specific problem in the heading. Using the sticky does not really address your specific problem. It may be worth posting a final image pointing out the issues you are concerned about.
I just can't help much with APP and how it handles calibration etc. Happy to advise about KStars related issues though.

Cheers,

Mike

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