I've found a very annoying visual bug with this plugin, and I have absolutely no idea how to fix it.

This is the color palette I'm using, with extra bright colors in there to demonstrate the problem.
For whatever reason, some colors are overriding each other, with values #111111 and #FFFFFF on grayscale patterns being rendered as the same color when they are not. I can't figure out for the life of me why this is happening- if anyone can help, it would be greatly appreciated!!

EDIT:

I've figured out how precisely the bug works- it starts off with everything being totally fine for one frame, then it breaks immediately after with #FFFFFF being overridden by the color that's being displayed in #111111.

Doesn't help me fix it, but if the plugin author or anyone more skilled in coding than me feels like taking a look...

Tested it in a new project as well- still happens, so it must be something specific to this plugin. It happens with multiple patterns and palettes, as well.

If I remember, how palette shifted colors are figured out is using 255/(width - 1) as the number of valid greyscale values for each shifted color (it doesn't shift the first color, which is always mapped to 0). That would give us 255/15 = 17. This bug would happen because  FF is hitting the max value and wraps around, and #111111, which is decimal 17 in grayscale, is still with the bound [1, 18] for the first mapped color. 

To solve, I would use greys in the middle of the target, so like #090909 and #F7F7F7 instead of #111111 and #FFFFFF respectively, if my logic is correct. (tbh it's been years since I wrote/looked at the code)

Huh, #090909 doesn't show up in the battle background now... let me try one a little higher.

EDIT: Yep, #171717 works! Thank you so much!!