New DWMWA_SYSTEMBACKDROP_TYPE in 22523 SDK, public Win32 API for Mica, Acrylic and their strange new 'tabbed' blend:
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Overall, does not seem to be changed from private API much. Caption text is opaque, I wonder if that's going to be fixed or custom slightly different titlebars all the way.
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Y'know, I'm surprised they haven't bothered to fix that yet, after causing that caption mess up in Windows 8.1. 🙃