Clear vs black in terms of light reflection? I've heard that clear things such as the gaseous components of the atmosphere or water reflect no light, and that is why they are clear. I've also heard that black things such as asphalt are such because they reflect no light. What is the physical reason for these things to reflect no light yet be totally opposite, such as black and clear? How can something be black or clear but have the same property of absorbing all visible light?
 A: There is something you should think about and then hopefully things become clearer for you:
The athmosphere is only "clear" in a rather narrow region of the electromagnetic spectrum (see the nice graphic on the wikpedia page). For most wavelengths, our air is unclear and little of the incident light reaches earth's surface.
Another useful example here is glass. Glass transmitts visible light, as you can see everyday. BUT: Glass does not allow ultraviolet (or infrared) radiation to pass through. This leads to two effects if you get cought in a summer traffic jam: 


*

*You will not tan. Tanning is induced by UV light, which cannot reach you uless you dangle your arm outside the window.

*The inside gets hot. Visible light enters the car and scatters into infrared (heat) radiation. But for this kind of wavelength, regular glass works like a mirror and the inside of the car can get very hot.


So, a black object absorbs all visible light, but might be translucent (or at least not completely obstructive) to other wavelengths. 
A: 
I've heard that clear things such as the gaseous components of the atmosphere or water reflect no light, and that is why they are clear 

Yes, "clear things" reflect light in very small percentage. But, they do reflect certain percentage of light falling on them. If they don't reflect that small percentage of light, you would have not been able to see them, they would have been invisible! 
You see things or this world of secrets, only because our eye is sensitive to visible light. When objects reflect light falling on them, that reflected light enters our eye which enables us to see things. So, there must be certain percentage of reflection from the "clear things" you see. And also you can see things behind the objects like glass, this is because, reflected light from the objects behind the glass pass through glass without getting reflected.    

I've also heard that black things such as asphalt are such because they reflect no light 

You can see any object with particular color, because they emit that particular color or electromagnetic radiation (leaving the rest).   

What is the physical reason for these things to reflect no light yet be totally opposite, such as black and clear? How can something be black or clear but have the same property of absorbing all visible light?

The reason is that "clear things" don't emit any electromagnetic radiation which is detectable by your eye, whereas the "black" objects (in your case) emit radiation detectable by your eye. 
A: Black objects absorb visible light. Clear objects let visible light pass through without absorbing it.
(Both black and clear objects reflect or scatter a little bit of the light, though.)
