You can use mental ray for Maya’s detail shadow map to render colored shadows in your scene. This effect is driven by the transparency color of the object, like raytraced shadows.

To render colored shadows with detail shadow maps

1. In the Scene View, select the light that you want to use to create a shadow. The light must be a point light, spot light or a directional light.
2. Open the Attribute Editor for the light shape node.
3. In the Attribute Editor, open the Shadows section, and set the Shadow Color.
4. Expand the mental ray section and select the Detail Shadow Map option under the Shadow Map Format attribute in the Shadows section.
5. Select the Use mental ray shadow map overrides option.
6. Render your scene in mental ray for Maya.