This is not really an bug issue, but an aspect of user convenience. It happens (e.g., in high key images that one does not see the white cursor line that separates the treated and the untreated parts of the image. It would be useful to be able to temporarily switch the color of that line from white to black when holding down a specific keyboard key. In this respect it would also be useful to be able to assign black or white as the default color of the line.
