I am wanting to know how this works. I think it looks beautiful on cakes!
Usually you pipe with royal icing (one flower at a time). Do the outline then take a dry paint brush and carefully drag icing from the inside edge of the outline toward the center of the flower. It's a little difficult to explain without pictures so the best suggestion would be to find a u-tube video or look in a cake decorating book. If you don't have any Wilton ones next time you're in a craft store browse through one of their books and see if you can find instructions.