inverted line drawing

In Paint when you select the iregular shape select (cut) the lines drawn are inverted. When I try to draw inverted using the line method ie line(currentx,currenty)-(x,y) drawmode=6, my line colors invert within themselves almost like a black and white bubbly color. Can anyone tell me how this can be done to get a smoothly inverted line with the image below?

I don't know what draw mode 6 exactly is, but using XOR should work, drawing the same shape on the same location using XOR again will restore the original image...