Is it possible to set a border to overlay (like in photoshop) <p>I am having a quite exotic question: I am currently working on a "borderless" WPF Application. I successfully removed the standard windows window controls and added my own. Now I wanted to add a border to the programm. But I don't want the border to have specifc color, I want it to be in some kind of overlay mode like when you set a layer in photoshop to overlay. You can see what I mean in an example:</p> <p><img src="https://i.stack.imgur.com/QBOcx.png" alt="Photoshop Mookup"></p> <p>I really want it to look like on the left. But unfortunately I really have no idea how. Basically what the overlay does is that it takes the background color and it makes it a bit darker. Do you have any suggestions what I could do?</p> <p>Edit: Here is a better picture of the effect</p> <p><img src="http://img.xrmb2.net/images/243147.png" alt="Photoshop Mookup2"></p> <p>Edit2 : So, as a short explanation because it may not be as clear as I have hoped: I am not talking about a semi-transparency. I know how to do that. The right box in both images uses that. It has a black-semitransparent look. While on the left I set the border to "overlay" mode. As you can see it gets darker but also a bit stronger in color.</p>