How many times have you painted a texture in Photoshop with pure black: 0,0,0? Well, doing so you destroyed your virtual worlds. Shame on you!
Black is not a color
First off, black is not a color. We all know this: it represents absence of light and therefore absence of color.
Now tell me: you have a red apple in a fully black room, with no lights. What color is the apple? If you say Black you'r right. And if you say red, you'r still right.
The apple is red, because that's its real color. The one we would perceive if it was illuminated. And the apple is black, because this is the color we are seeing now.
In 3D graphics the red apple is the one we texture and provide to the software. The black apple is the one the software computes for us.
So far this may seem a sterile post, but bear with me for a minute more. What would happen if we took a black apple and placed it in a luminous room? What color would it be? Black, only and forever black.
When you use 0 as a color, you are hijacking your renderer's ability to do its work. The surface you created has no equivalent in nature because it can absorb any amount of light shining on it.
Any number multiplied by 0 is 0
Again, this is common knowledge, yet pure black keeps being used in texture maps because we often forget that the whole lighting in computer graphics is performed multiplying values. This is something compositors know all too well, but CG artists forget.
Apart from black, there's a more subtle issue here — even if you avoid black, other colors may still harm your rederer. A yellow tone with 0 in the blue channel, for example, will kill all blue contribution. No matter how strong your blue sky is.
In short: say no to 0 values.