Keith,
I just upgraded to Windows 10, so this may be some sort of update issue. I used settings to toggle multi-monitor task bars on and off. When I press "Reset All Taskbars", I get a proper unhidden task bar, but when I turn on auto-hide, the task bar goes transparent just as show in this picture below. I am use Beta 9 of version 8.

Here's the trouble shooter output.

Damn, you're good. It helps when you get the troubleshooter data, eh?

Windows 10 Settingstab had Customize Task Barcheck with the Taskbar Lookset to Transparent.

Setting to Opaqueor Glass(with a reasonable opacity) solves the problem. One wonders where that default value of transparent came from, or if anyone thought that made sense. During the upgrade from Windows 10, Windows 10 insisted I uninstall the version of Classic Start Menu I was running, so I installed the current version after the upgrade.

In any case, I guess this handles my issue.

Thanks!