Black is the densest color. Actually it is all colors totally absorbed and in its total absorption it reflects no wavelengths.
Black gives structure, it creates a frame and feels grounding.
As for clothes, I like tend to wear more black in August than in January or April. I find layers of black easily too heavy on me, while a totally black looks super elegant when there is a little bit of collarbone or bare ankles involved.
In winter though, for as long as I can remember, fitting black turtleneck sweaters in thin merino or cashmere have been one of the key pieces in my closet. Lately I have been wearing them mostly with white jeans or a pair wide-legged navy corduroy trousers by Acne Studios.
Black is essentially the absence of light, a total darkness. And along with daylight, we need a certain amount of dimness too, to think clearly and be fully ourselves.
For more about the significance of shadows here.
My black moodboard here.