you can put your textures inside folder with mod and use something likes this:
var customImage = Image.new()
customImage.load(globals.modfolder + location of your custom textures
createcustomtexture.create_from_image (customImage)
i wasnt able to test it in practice because i only have ideas for custom potions, but whole potion system annoys me a little and i dont wanna mod without ideas i could consider as "good"