It's not fully negative. Just black to white, which makes patches and speckles of white in images where it shouldn't be.
Here, I screenshotted the native reader and used my phone to take a picture of the same page open in Coolreader.
Native Reader:
https://i.imgur.com/XBspsZG.gif
CoolReader:
https://i.imgur.com/3IIDxeK.jpg
EDIT: And upon further investigation, epubs made with Kindle Comic Converter render just fine. It's only mobi files that are an issue.