@Override
		public void paintBorder( Component c, Graphics g, int x, int y, int width, int height ) {
			if( c != null && c.getClass().getName().equals( "javax.swing.JTable$BooleanRenderer" ) ) {
				// boolean renderer in JTable does not use Table.focusSelectedCellHighlightBorder
				// if cell is selected and focused (as DefaultTableCellRenderer does)
				// --> delegate to Table.focusSelectedCellHighlightBorder
				//     to make FlatLaf "focus indicator border hiding" work
				JTable table = (JTable) SwingUtilities.getAncestorOfClass( JTable.class, c );
				if( table != null &&
					c.getForeground() == table.getSelectionForeground() &&
					c.getBackground() == table.getSelectionBackground() )
				{
					Border border = UIManager.getBorder( "Table.focusSelectedCellHighlightBorder" );
					if( border != null ) {
						border.paintBorder( c, g, x, y, width, height );
						return;
					}
				}
			}

			super.paintBorder( c, g, x, y, width, height );
		}
Border for focused unselected cell that uses margins and paints focus indicator border.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatTableCellBorder.java