Use same color, No need to reduce it.

Go for it. Dont reduce the paint. Your ceiling may look lighter than the walls anyway. I have several rooms done like that, and even though it is the exact same paint as walls, the ceilings always appear one shade lighter at certain times of the day. I love them done that way.

The same color blue is one good option, though you could consider another color that coordinates with other elements of the decor and also coordinates with that particular shade of blue. Rather than lighter, a darker color may look even better. Either way, it is a great idea compared to just leaving the ceiling white.

Terracena Model Master Bedroom · More Info