Value

Achromatic Color- The use of blacks and whites and everything else in-between.

Hurwitz, Lake. The White Vulture. 2010. DeviantArt. Web. 2 Nov. 2012.
<http://lakehurwitz.deviantart.com/art/The-White-Vulture-184759238>.

As you can see above, the whole image was done in achromatic as it is all black and white.

Value pattern- The amount of variations of lights and darks, independent of colors used.

Arias, Gonzalo. Malinche. 2012. DeviantArt. Web. 2 Nov. 2012.
<http://genzoman.deviantart.com/gallery/#/d5eh2la>

Value Emphasis- High contrast in one area to draw the user's eye to that spot.

Gavrilenko, Viktoria. Nymphs - Lyth and Yana. 2012. DeviantArt. Web. 2 Nov. 2012.
<http://viccolatte.deviantart.com/art/Nymphs-Lyth-and-Yana-288176827>.

As you can see, your eye is automatically drawn to their faces and clothing as the high contrast of the orange stands out against their skin and the blue background.