It is like "do it in your style" from splinterlands game. And, of course, my nymphs are absolutely different. I leave the skin, hair and dress colours, but generally she is all my imagination.
And that is especially obvious with my hardest part, which is anatomy from imagination. Usually I construct it all in my head without any reference. It is very hard and I can spend lots of time thinking about muscles or how light falls, but I am sure it is very useful for my progress.