cutebunnyThey're two different switches. Green's are very heavy switches, both clicky and tactile. A lot of people don't really like heavy switches. Clears are not nearly as heavy, are tactile but not clicky, and are considered to feel more tactile than Browns.
thebrassthiefTo add to this.
http://www.keyboardco.com/blog/index.php/2012/12/an-introduction-to-cherry-mx-mechanical-switches/
Greens are essentially a stiffer blue.
Clear switches have the largest tactile bump.
You can see in the GIFs how the tactile bump is less pronounced in the brown and blue switches when compared to the clear.
Also notice in the blue switches GIF the extra white piece.
The extra white jacket hits the bottom, creating the click.
[the same happens in green switches]