Sure, and it's not hard. Color objects have opacity as part of their properties. It's referred to in the documentation as the alpha value.
Just create a Color object with an alpha value of 255, and the color of the object behind will show completely through.
Note it is *not* possible to do this with an AWT Frame or other top-level window objects. Frames are "heavyweight" components which include by definition an opaque background. You can change the alpha value on a top-level window, but it will have no effect.
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Michael Ernest, co-author of:
The Complete Java 2 Certification Study Guide