How to disable taskbar transparency in Windows 8 desktop?

You can do it if you switch to the Aero lite theme, see How to Enable Hidden “Aero Lite” Theme in Windows 8 and Later? and How to disable transparency in Windows 8's taskbar?.

1. Open C:\windows\resources\themes\*.theme with notepad.

2. Under the key [VisualStyles] change the pointer to Aero.msstyles to point to AeroLite.msstyles.

3. Save the file (you can't actually, so save it to another location).

4. Double click your .theme file

Now your Taskbar is no longer translucent:

To apply it on the current theme, see Will's answer below.

The downside of these approaches is that the Aero lite theme looks different (take a look at your minimize-restore-close buttons and etc) from the normal Windows 8 Aero theme.

Note that if you have personalized your theme it will be located here:

C:\Users\[User]\AppData\Local\Microsoft\Windows\Themes

I edited the file directly and it worked.

Edit of previous version.

This doesn't actually fully work. Windows that are moved to slide under the taskbar are still visible. This bothers me every time I see it, so I'll continue to seek a complete fix (to turn off transparency for the desktop taskbar in Windows 8).