:-)

I agree, but I like its icons.

Thanks for the reply. No, that wasn't it. Eventually I discovered that Panel Options -> Configure Panel offered a way to remove any of the icons.

As for the transparency, it's a feature of the icon set I chose, GNOME. Most of the icon sets include a transparent Audio Volume. Breeze and Breeze Dark are the only ones (of the default sets) that include a visible one. I would think it's a bug.

right-clicking on the icon does not provide a menu option to remove it.

May be your widgets are locked. Try this:
On the panel, click secundary mouse button, Unlock widgets.

I added a number of icons to the panel, including Konqueror. However, I'm not impressed with Konqueror, as it displays an Undocumented Error upon starting, something to do with the home page, I guess. So I thought I'd delete the icon from the panel. But unlike with Cinnamon or MATE, right-clicking on the icon does not provide a menu option to remove it. Dragging it does not work either. How are icons deleted from the panel?

I actually read the release notes, so I was able to get sound to work. But when I placed Volume Control on the panel, the icon was transparent. I know it's there because I can click on it and get it to display. Any hints on how to make it visible?