By default, when working with transparent objects in InDesign, the characteristics like blending mode affect all objects that sit below in the stacking order. Sometimes, this isn’t the look you are hoping to achieve. That’s where two little options in the Transparency settings come in handy. To work with an object’s transparency, open the Transparency panel (Window > Effects) or the Transparency pane of the Effects dialog box (from the fx button in the Control panel). No matter which you’ve opened, set the transparency (opacity) for each object, as well as a blending mode. There are two additional checkbox options—Isolate Blending and Knockout Group—that allow you to control which items interact, or don’t, with which other items. For either of these to work, some of your objects will need to be grouped first.
Use this option when you want to limit which objects will be affected by transparency blending modes. For example, if you want your top two objects (like the blue and yellow objects in the screenshot example) to interact with each other, but not with any background objects, select and group those two objects. Next, go to the transparency options and select the Isolate Blending option. With this option selected, the objects within the group react to each other’s transparency effects as before, but the items below the group are not affected by any blending modes assigned to objects in the group.
This doesn’t mean that the lower objects aren’t still visible through the transparent objects, just that the blending modes are ignored. If you have objects in the group that have the Multiply blending mode applied, the objects below the group will still show through, but will look as if the basic Normal mode has been applied. If the grouped objects only have the Normal mode applied to begin with, the difference might not be very obvious. Setting the Overprint Preview in the View menu will give you a more accurate representation of transparency and how each object will react.
The Knockout Group option does pretty much the opposite of Isolate Blending. Choosing this option forces each item in the group to be knocked out by higher transparent objects within the same group. So, if a transparent item is sitting on top of another item in the group, not only is any blending mode ignored, but the lower items become obscured. However, all items below the group itself do interact with transparent objects in the group. Unlike Isolate Blending, where only blending modes are affected, the items below the group here are affected by blending mode as well as opacity amount.Tags