You say this is invisible in the day. Is it really invisible? Be honest.
These murals are invisible (or virtually invisible) on a light and white surface. In 98% of the ceilings I’ve done I would say absolutely invisible by day. Some of the largest stars, or shooting stars may be SLIGHTLY visible during the day on darker surfaces or if your room is dimly lit.
If you have a ceiling that is colored, not white we can talk about the pros and cons of painting the ceiling white first The main “con” in painting the ceiling white first is probably that painting a ceiling is an inconvenience, and you may prefer a darker color, say, for a theater room. The main “pro” would be a brighter and longer lasting glow as well as assure complete invisibility during the day. That being said, I have done these ceilings on numerous medium dark colored ceilings and the customer was very satisfied. Light colors are still virtually invisible by day and glow well through the night.