By default Toad highlights the matchin open and end parenthesis in the editor when the cursor is in the middle of the two. The setting for this is under View | Options | Editor | Behavior | Syntax Highlighting for ().
But even when this setting is disabled, the border outline of the parenthesis are still displayed. It still shows the dotted line around it, though the rest of the settings (i.e font and background color) is disabled.
How do you completely disable syntax highlighting for parenthesis?
This is also an issue for "Current Block" setting.
Manually set the boarder setting to show no lines.
Waiting for fix in a future version of Toad for Oracle.