With the latest changes and addition of:
Controls.DropAreaIndicator fg=XXX
Controls.DropRowIndicator fg=XXX
the Panels Configuration panel has gotten more precision when dragging elements between panes.
When you drag an element to an 'allowed' area, it is looking quite clear and precise now.
But when you drag it over a 'not-allowed' area, the present lines there are still highlighted and flashing, which makes it all look a bit nervous.
Since the mouse cursor is already transformed into a 'stop' or 'forbidden' symbol, and the vertical DropAreaIndicator's absence at those locations should also be clear, this additional highlighting and flashing of the lines where you can not drop the element is a bit superfluous and makes a nervous impression.