Value refers to dark and light.
Value contrasts help us to see and understand a two-dimensional work of art.
This type can be read because of the contrast of dark letters and light background.
Value contrast is also evident in colors, which enables us to read shapes in a painting.
Value in Fine Art
Metzinger's painting has strong value contrasts as can be seen in a black and white version of it on the right. The painting is cubist in style with angular fractures and shapes. Follow the visual movement from the bottom right over a light-valued visual path upward to the top left sail, which is the focal area. A high contrast in value can help define a focal point.
Source: Elements and Principles of Design: Student Guide with Activities, published by Crystal Productions
Value in Graphic Design
Cyclone Self Promotion
Dennis Clouse, Traci Daberko
But first, let's look at value. The poster is very colorful but low-key in value, meaning that except for black, the values are overall similar. Because of the color palette, it does not run the risk of being anywhere near monochromatic. Compare the original on top with a black-and-white version below it.
Source: Design Basics for Creative Results by Bryan L. Peterson