I have taken views of many websites and books about how objects have color and they offer only one explanation: it's because they absorb all other colors and reflect color of only one wavelength and black is so because it absorbs all colored wavelengths of light. But if it absorbs all colored wavelengths then shouldn't it be invisible?
$\begingroup$ In the loose sense of the word, if you meant that your eye receives no photons coming from an object, then yes, it is invisible. However you'd know if you were looking at such an object because it would be pitch black. $\endgroup$– NeilMar 18, 2016 at 13:07
$\begingroup$ @Neil,Does it mean that black is something invisible or are all invisible objects in the universe all black? $\endgroup$– bzalMar 19, 2016 at 4:17
1$\begingroup$ The color black doesn't exist. It is only the absence of perceivable light. So, in a sense, black is invisible. The objects themselves not emitting light are not necessarily invisible. It isn't enough that invisible objects don't emit light, but they have to allow light to pass through them. So no, "invisible" objects aren't black anymore than water is black. $\endgroup$– NeilMar 21, 2016 at 7:53
When we say an object is invisible we normally mean light passes straight through it. That means it doesn't reflect any light and it doesn't block any light. Something that is black doesn't reflect any light, but it does block light so we can see it by spotting what it obscures.
For example in astronomy we can't see objects if they are so dark they reflect too little light to detect. However we can detect them if they pass in front of a star and block it. This phenomenon is called occultation.
$\begingroup$ What about black in emissive systems such as televisions? Are they also occlusion? $\endgroup$– bzalMar 23, 2016 at 1:56
$\begingroup$ @bzal: yes, the black areas of the screen occlude the wall behind the TV. They would only count as invisible if you could see straight through them to whatever was behind the TV. $\endgroup$ Mar 23, 2016 at 6:03