A particle can be assigned to a group.
To use different particle groups in an emitter, drag the groups you want to use into the Groups to Use list in the xpEmitter.
Alternatively, you can click the Create and Add Group button in the emitter Groups tab; this will create a group and automatically add it to the Groups to Use list.
If no groups are present in the list, all particles will be in the default group and will have the color and shape found in the emitter.
If more than one group is in the list, new particles will be assigned randomly or sequentially to one of the groups, depending on the emitter setting.
Note: More than one emitter can use the same group if you wish.
You can add as many groups to a scene as you wish but the group must be created before you can assign a particle to it.
To create a group, add an xpGroup object to the scene.
This can be done using the main plugin menu, or the system object, or in the Groups tab in the xpEmitter.
A group is not specific to a single emitter; you can have multiple emitters all emitting particles in the same group, if you wish.
xpGroup, General tab menu settings.