Color differences in importing/exporting large sprites

[brassmaster2357]

Describe the bug

Problem

I'm trying to resprite Peppino in Pizza Tower (on and off since November, it is obviously a Sisyphean task) and having a lot of trouble with larger sprites.
Editing Peppino himself in the game works perfectly fine, the clothing colors are replaced as they should be.
However, when importing larger images like ranks into UTMT, edges of lines and lines themselves have very slightly different colors. (#010101 instead of #000000, #FEFE40 instead of #FFFF40)

Demonstration

Creating a replacement for the final D rank frame

The color inside of the letters is #FFFF40, the clothes color, all the way through - the lines are #000000 as well

Then, importing and exporting the image causes colors to be changed. Running the game with these large imported sprites causes colors to not be replaced.

Selecting #FFFF40 in the exported image shows pixels that were that color, but changed.

For my input, I suspect this is an error with importing images, or there is a setting in UTMT that I haven't found yet. Apparently there is a solution, but nobody has written about it from what I can find.

Reproducing steps

1. Make a large sprite (ex. ranks, boss profile), correct resolution and such
2. Import image
3. Export image, colors have changed

Setup Details

1. UTMT v0.5.1.0
2. Windows 11
3. paint.net