Merge modes for grouped objects
When you group objects, the Pass Through merge mode is automatically assigned to the new group. With the Pass Through mode, the group has no merge properties of its own. Instead, the merge modes within the group affect the appearance of object colors within the group as well as any underlying objects. If an adjustment lens or another effect is applied to the group, it affects the colors of underlying objects or background.
You can change the merge mode for the group to create various blending effects. For more information about merge modes, see Merge modes.
The original image (left) contains grouped objects. A lens effect was applied to the group (right). The Pass Through merge mode was applied to the group so the lens changed the gray background behind the group as well.
To choose a merge mode for a group
You can also choose a merge mode for grouped objects and adjust their opacity from the Group properties dialog box.