right now, (early afternoon, on a cloudy day) part of my white ceiling are a darker grey than my grey walls. at every joint where the wall meets the ceiling, its quite clear that the walls are darker, but the diffused soft light leaves the ceiling, not sparkling, but a gradient grey (whiter closer to the windows, darker and darker, as you move further away)

--and while it is cloudy, its still bright--so the grey wall that is opposite the bright yellow wall looks moss green instead of grey. (the grey is a bluish grey)

i thought a good deal about the colors for my walls (and ceilings) my main (living/dining/computer room) ceiling color is an artic (blue) white. -(the bedroom ceiling are blue--pale sky blue--but most definatelly blue!)

In the daylight, its obvious the yellow (computer room) is a pure tone--a true yellow. but at night, it looks ever so slightly yellow green- the relected light of the living/dining room overwhelms the yellow--especially when only the low watt energy saving florescent lights are on--with the cool blue light they emit.
but in the daylight (or with the (yellow) incandesent lights on, the yellow can over power the grey,(at least in one corner) and make it look like a grey/green (pale moss/sage in tone!)

i love that i change the colors of the walls simple by turning on (or off) key light fixtures.

i am tone deaf (as much as enjoy music, i realize this) but i have something like perfect pitch when it comes to being able to 'see colors'.