The color of the light source directly affects the hue on the light side of form. Within the cast shadow, it causes the illusion of the light-source complement. As Reilly illustrates in his notes below, a red light on a white object would give the white a red cast in the light, and the cast shadow would look like blue-green.
Paint the object in the light with it's local color plus the color of the light source.
The cast shadow is the local plus the complement. It's chroma should only be half as strong as the surrounding light area.
The chroma in the cast shadow gets slightly weaker as it comes towards the viewer, and stronger as it recedes from view.
© John Ennis 2011
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