Originally Posted by Mythic
White is the combination of All Colors
Black is the combination of All Pigments
Pigments absorb light and reflect a portion of the spectrum. this portion translates into what we see as "Color"
The more the pigment absorbs the darker the "color" we see.
Very white paint absorbs very little light so reflects as white and bright.
Black paint the opposite (which is why to me a smooth black finish is sooo cool, like looking into an osidian mirror - err too much?)
In addition to the spectum of light that is absobed/reflected there is also the luminosity or how much of it is reflected.
Again Bright white reflects alot of light black little. Grey absorbs alot of the spectrum but has higher luminosity.
Richer Color paints tend to darker because of how much and what they absorb to create the deeper colors we see.
(My physics of light is a bit simplistic, its been a reallly long time since I had this crap)
Also it depends on what you have in mind when you think of a color in the same family.
To some Navy blue is Blue to others its Robin's egg. both would consider Midnight dark and Sky light, but the one thinking of Robin's egg might see slate blue as dark where the guy thinking of Navy would say light.
It's very much subjective.
A MUCH more technical version of my explanation. LOL I admit you're the first person I've ever met that knew about this. Most people just look at me like I'm nuts. haha