Apple Motion 4 - Manual (Page 1239)

When Shading (the visible effect of lighting) is disabled, shadows behave differently.
Rather than being multiplied with the object upon which they are cast, the shadow’s
color and opacity are controlled only by the Shadows settings in the Light tab of the
shadow-casting light’s Inspector.
Shading enabled Shading disabled
This enables you to create shadows of any color or opacity, from traditional dark shadows
to brightly colored or even white shadows.
1239 Chapter 18 3D Compositing