I'm using DwmExtendFrameIntoClientArea in my WPF application to get the glass effect. This is working fine. What I'd like to do is change the colour used for the glass -- I'm writing a countdown timer, and I'd like the window to be the normal glass colour most of the time, and then to go red (but still with glass) when the time runs out.

I found this question, which talks about how to apply a gradient glass, and that works fine when picking a different colour. Unfortunately, the borders are not coloured appropriately.

When I turn off the borders by using ResizeMode="NoResize", then I end up with square corners. I'd like to keep the rounded corners.

I looked at creating an irregularly-shaped window, by using AllowTransparency="True" and that works fine, but doesn't look like an Aero glass window. It looks a bit flat.

So: my question: how do I create a window in WPF that looks like Aero glass transparency, but uses a different colour?