Adobe ILLUSTRATOR CS2 User Manual page 251

If you want to change the opacity of a fill or stroke, select the object, and then select the fill or stroke in the
Appearance palette.
Set the Opacity option in the Transparency palette or Control palette.
2
To select all objects that use a specific opacity, select an object with that opacity, or deselect everything and enter the
opacity value in the Transparency palette. Then choose Select > Same > Opacity.
If you select multiple objects in a layer and change the opacity setting, the transparency of overlapping areas of the
selected objects will change relative to the other objects and show an accumulated opacity. In contrast, if you target
a layer or group and then change the opacity, the objects in the layer or group are treated as a single object. Only
objects outside and below the layer or group are visible through the transparent objects. If an object is moved into
the layer or group, it takes on the layer's or group's opacity, and if an object is moved outside, it doesn't retain the
opacity.
Individual objects selected and set to 50% opacity (left) compared to layer targeted and set to 50% opacity (right)
See also
"About the Transparency palette" on page 243
"About targeting" on page 420
"Using the Appearance palette" on page 419
"Printing and exporting transparent artwork" on page 484
To create a transparency knockout group
In a transparency knockout group, the elements of a group do not show through each other.
Group with Knockout Group option deselected (left) compared to selected (right)
In the Layers palette, target the group or layer you want to turn into a knockout group. (See "About targeting" on
1
page 420.)
2 In the Transparency palette, select Knockout Group. If this option isn't visible, select Show Options from the
palette menu.
ADOBE ILLUSTRATOR CS2 244
User Guide