http://www.daliahammar.com/design/y11e28ecn8508z80m9njl8pt5w9zkm

This screen printed poster uses colors to create contrast such as black & white as well as blue and black.

This is a lithograph on paper in which we can see the use of light and shadow to create contrast.

This flashlight uses the colors of yellow & black to create contrast which successfully shows light vs dark.

Thumbnail sketches are important in that they allow you to refine your ideas and really get a better understanding of what you want to create prior to working on the final version. A designer is able to loosely put ideas on to paper without the stress of making something totally perfect.