Look up Serdar Yener tutorials on here, he has a great stamping video he shows with a carrot. If you watch it, you could easily do something similar using celery or romaine lettuce stump and stamp onto your fondant.
The picture is obliviously not being used for food, but it was the only one to get my point across. (Or explain it rather) once you modify it to fit your needs in the cake world, it’s a pretty great trick to have. Then you don’t have to paint at all.
Hope this helps!
Here is a cake by someone else using this ideal method.
