HOW TO CREATE CUSTOM GRADIENTS IN GIMP
https://www.sl-inspiration.com/2018/05/how-to-create-custom-gradients-in-gimp.html
Creating a custom gradient in Gimp does not need to be a complicated process, and once you have a grasp of the basics each gradient can be used in your own designs. The wings of the above butterfly here were filled with a custom gradient, and after we show how to create a custom gradient in Gimp, we'll walk you through how the image was put together so you can make your own butterflies if you want to.