Hello! I'm actually just a silent lurker in this forum, but I saw your question and I think I can somewhat help you with that. Anyway, I found this artist named Lee Yong Je while browsing at instagram last night and I found him because he tagged the drama in his most recent post as shown below: He also posted a clip of the drama's 13th episode in his IG and a part of that post's caption states that his artwork was featured in that episode as Lee Sol's graduation artwork. Now, I can't confirm if he also did the bubble paintings because the only artwork that he acknowledged that was his was the one that was shown at episode 13. However, it seems that most of his artwork are also about bubbles, which look quite similar to the bubble paintings featured in the drama.