Using Imported Textures as Templates for Other Imported Textures

I recently tried MCreator again and could've sworn that this was a thing before, but apparently it wasn't, unless the feature was removed. But basically, it would be so much easier to make and edit textures if you could use textures you've uploaded and layer them with other uploaded textures to copy the colors from one to another, or for any other reason. It's been very hard for me to do this, because GIMP is too hard and confusing with pixel-by-pixel editing, and I've been at it four hours on end.