Alright since feedback is requested, I do have a couple more niche questions, if you don't mind.
Importing multiple textures and maybe exporting them all with a prefix/different directory with the same name would be pretty convenient, but you already mentioned that here and in other comments :p
Saving brightness/exposure/contrast/etc as a default / saved config would be convenient, probably a little niche tho.
When loading all the palettes with the palette+ downloaded the program does lag/freeze very briefly even with a decently beefy pc, I HATE to backseat dev especially since I dont know the inner workings of the program but if you don't mind me making some minor assumptions, maybe wrapping the loading of palettes into an async task to help with the brief freeze could help, and caching them during runtime if you dont already might prevent it from lagging on subsequent loads although that would be choosing to be a biiit more memory heavy.
I'd like to emphasize again that I love the program and its helped me a ton, these are just minor requests/nitpicky features