Black
In colour theory black is often described as the absence of light. This is not necessarily bad - just a fact of life... like night-time. however, black hides things from view. That's part of its function - it makes things disappear. Therefore wrongdoing is more likely to take place (for instance) under the cover of darkness where nobody will see it. So black gets a bad reputation just because of when and how it is used.
In fact, the colour is also strongly associated with mourning throughout the Western world... where the general view of death has been that it marks the 'end' for a very long time. Take a look at Eastern cultures which hold a widespread belief in reincarnation and the colour of mourning is white... for the transcendance of the spirit.
The reason that mourning tones were originally designated as black is because the mourner was expected to retire from the world for a time in order to cope with their grief... so black 'disappeared' them.
Black comes in useful for all kinds of things when applying colour therapy and balance principles - it induces sleep, eases insomnia, can reduce pain and is sometimes useful when fdealing with extreme shock.
Psychologically, it's a colour often worn during transitional times when the wearer is not quite certain where they're going, or when they are going through a period of change - that's why it tends to be so popular with younger people who are establishing their place in the world.
Because it hides things from view it creates a semi-mystical effect... the person wearing all black comes across as mysterious and inexplicable... but in fact interpretively it's much more important to consider what else the person chose to combine the colour with in order to learn about their inner motivations...
