Not the GP, but inspired by your question I tried asking ChatGPT to create similar coloring sheets. The results seem suitable for coloring. Here's one prompt: "A simplified line-drawing coloring sheet of a dog flying an airplane. The drawing is in clean black lines on a white background, with minimal details and clear, bold outlines."

Later: The prompt worked with Imagen 3 on Gemini Advanced, too:

https://g.co/gemini/share/fd023da84cb2