Colour Values...

What is the 'importance of value in a painting'?  A color's values create our perception of three-dimension and perspective. Here is a good explanation.

Value is the lightness or darkness a color or hue. Believe it or not, value is more important than color to the design and success of a painting. Here's why: Value is used to create a focal point within a painting or drawing.

Understanding Value and Tone for Better Painting

www.artistsnetwork.com/.../understanding-value-and-tone-for-better-painti...

http://emptyeasel.com/2008/12/09/two-reasons-why-values-lights-and-darks-are-so-important-in-paintings/