If you can’t get Photoshop, or if you’re worried about viruses in a free version, you can try Affinity—it’s quite good for what you need and it’s free to use.
Thats what I use, and it doesn't seem to work the way I need it too.
I might as well post images here for references on what I'm trying to do lol.
I'm wanting to swap the hair color while preserving the sheen effects that they had put into the Material edit, and without getting rid of the ear color either.
Changing these two colors to the corresponding arrows.
The end product of what I want it to look like is something like this. I've already got everything else sorted for it, I just need the hair and tail colors to swap, but they can only be swapped using the ME because of how the author made it.
The website the other person posted should also be able to do the methods I just mentioned and the methods I'll explain next, because it seems to have most of the functions. However, I switched to Photoshop from that website a while ago, so I can only use Photoshop to explain.
https://www.photopea.com/ This is the method of using a masking film
I tried using gimp originally, but it didn't seem to quite help with what I'm trying to aim for either, as I'm trying to edit specific colors without damaging the main look, and whenever I uploaded material edits from gimp, the color would mess up somehow, and not sure why. In the above quote are images I'm using for reference on what I'm trying to aim for.