The edge color should be in contrast to the surface color to have better visibility
currently there is only one color option to choose for edge color , what i am proposing is two colors based upon the brightness of the surface color. if it is below 50 then edge color should be 75 brightness and if the surface has brightness above 50 then edge brightness should be 25. see the image to have more clear idea
Currently only pure black and white colors are useful in screen. if we use other colors the edges dont appear clearly and we struggle to find them for doing various things.