3D Compositing with Action > Action: The Particle System > Customizing the Particle Stream >
Setting Geometry Properties

You can use the Particle Geometry menu controls to add colour, specular highlight, shine, and transparency to all particles. To access this menu, click the Geometry tab in the Generator menu.

Use the available particle geometry controls to affect the particle stream, whether it is a surface or a geometry. The controls behave in the same manner as when using with the Geometry menu for a 3D model. See Working with 3D Geometry.