Value:
“Value is defined as the relative lightness or darkness of a color. It is an important tool for the designer/artist, in the way that it defines form and creates spatial illusions. Contrast of value separates objects in space, while gradation of value suggests mass and contour of a contiguous surface.”
Source: Color, Value and Hue – Art, Design, and Visual Thinking
char.txa.cornell.edu/language/element/color/color.html
My definition: The relative lightness or darkness of a color.
Gouache:
“ɡwäSH,ɡo͞oˈäSH/
noun
a method of painting using opaque pigments ground in water and thickened with a gluelike substance. “
Source: Google dictionary
My definition: type of paints that use opaque pigments combined with water and thickened with a glue type of substance
