She probably kept the background sketch layer and then when she finished coloring the whole thing just merged all the layers except that one and cropped out everything but the circle revealing the rest of the sketch behind it. Actually a really cool idea
So I sort of have a lot to say about this because of how much I love it. I'm not sure, but out of all your works, this one stood out the most to me. Methinks it may have to do with the fact that I find white hair overwhelmingly beautiful and that the boy's design is different from what I'm used to when I see couple's art. I really love the body language and the subtly of their facial expressions. And I also appreciate the braided hair because god knows it's a bitch for me to draw, pardon my French. Also the cat. I like the cat. He is cute. Is there a story about these two, because I would really like to know their story.