Unfortunately, I can confirm this. But, it seems to only happen with PNG images that have a reduced palette.
I have a test kepub (from DNSB I think) with lots of different things in it. This has six versions of the same image in it. The only one that has a problem is the grayscale PNG with 16 levels. Experimenting with the calibre conversion from a CBR to kepub, if I turn of the image processing, everything is OK. If I have this on and convert to PNG, the images are black.
So, the workaround is to either turn the comic processing off, or convert to JPG.
I have reported this to Kobo with my test case.
|