Image color inversion in night mode seems unnecessary. It's also really awkward, particularly when an image's colors don't invert nicely or with good contrast. This forces the user (me) to switch off night mode and suffer the sudden bright white screen glare of my non-e-ink display just to be able to get meaning from an image.

It is not unusual for epub and mobi to use images for charts and tables, for example. And colors frequently invert weirdly, such that perceivable data is lost.