Part of why you don't see colors in astronomical objects through a telescope is that your eye isn't sensitive to colors when what you are looking at is faint. Your eyes have two types of photoreceptors: rods and cones. Cones detect color, but rods are more sensitive. So, when seeing something faint, you mostly use your rods, and you don't get much color. Try looking at a color photograph in a dimly lit room.
As Geoff Gaherty points out, if the objects were much brighter, you would indeed see them in color.
However, they still wouldn't necessarily be the same colors you see in the images, because most images are indeed false color. What the false color means really depends on the data in question. What wavelengths an image represents depends on what filter was being used (if any) when the image was taken, and the sensitivity of the detector (eg CCD) being used. So, different images of the same object may look very different. For example, compare this image of the Lagoon Nebula (M8) to this one.
Few astronomers use filter sets designed to match the human eye. It is more common for filter sets to be selected based on scientific considerations. General purpose sets of filters in common use do not match the human eye: compare the transmission curves for the Johnson-Cousins UBVRI filters and the SDSS filters the the sensativity of human cone cells. So, a set of images of an object from a given astronomical telescope may have images at several wavelengths, but these will probably not be exactly those that correspond to red, green, and blue to the human eye. Still, the easiest way for humans to visualise this data is to map these images to the red, green, and blue channels in an image, basically pretending that they are.
In addition to simply mapping images through different filters to the RGB channels of an image, more complex approaches are sometimes used. See, for example, this paper (2004PASP..116..133L).
So, ultimately, what the colors you see in a false color image actually mean depends both of what data happened to be used to be make the image and the method of doing the mapping preferred by whoever constructed the image.
The answer to your question is the obverse of it: we assign a color to an object based on the wavelengths which are reflected to our eyes (or in the case of filters, transmited to our eyes). That means other wavelengths are absorbed. The absorption of wavelengths is based, primarily, on the chemistry of the object.
Red dye applied to cotton cloth is a chemical whose molecules absorb less red light than other wavelengths, hence the red wavelengths are more intense than other wavelengths in comparison to the light from other objects. Similarly for blue, green, yellow, etc objects. Most objects of colors don't absorb all the energy of other wavelengths; they just absorb less of certain wavelengths, and we assign a color name based on the modified mixture reaching our eyes.
In fact, the "colors" surrounding each other can modify our interpretation of what color we see. (Search for "color optical illusions". There are fascinating examples.)
Regarding absorb and reflect: they mean exactly what you think. The energy of an EM wave is taken into a molecular structure and not released as the same wavelength (absorption) or it is released as the same wavelength (reflection or transmission).
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the darker the color the more absorption of sunlight , and since the process is reversible there will be more emission for darker colors.
In skin, the dark color denotes a lot of melanin, and melanin is the defense of the body against ultraviolet radiation from the sun. It does not allow it to penetrate and destroy the lower layers. The first evidence of damage is sunburn.
This is a biophysics question. I believe it is due to the lack of melanin which allows penetration of ultraviolet and mutation of lower level cells that can turn cancerous.
Not that I know of. The use of dark colors when one wants to absorb sun energy (( as in sun water heaters) and light when one wants a lot of reflection (as on rooftops) is of course general.