Taken from the yaru theme of Ubuntu and Windows 10. Both have the black panel/dock.

The effect is this, a small modification is enough. It has a higher contrast and to me personally it looks more elegant / beautiful.
What do you think?

Where are the background color settings for the Kubuntu panel only?

Thanks for taking the time to answer me.
In fact, the change isn't worth the extra maintenance, because it's a slight improvement.
Maybe the change could be made upstream on breeze-dark?