Even if all the colors are black and white, I've found it that you MUST have the canvas file be completely grey scale. I don't know how FireAlpaca works, but I know that in GIMP, when starting a new project, you can choose to either make a RGB project, where you can have all the color you want, or a grey scale, where even if you select a color to creat with, it will come out grey. If you make it in a RGB format, even if all the colors are indeed in full black and white, it will not load into the game, I've noticed. It must be created on a grey scale project- so that even if you pick a color to color with, it will just come out grey.
Edit- You posted right before I posted - 3- XD