set objectboundarycolor
set objectboundarycolor= { colorname | #rgbspec}
This option determines the color used to display object boundary borders in the Edit window. The default value for this option is gray5. The value is either a named color or an RGB specification preceded by #. If objectboundarycolor is set to values of inherit or default, the boundaries are displayed with the default color of text in the Edit window (The default color is set with the window_setcanvasforeground attribute or determined by the operating system default if otherwise not set.)
Examples:
set objectboundarycolor=inherit
set objectboundarycolor=blue