A black line follower would assume that if its sensors sensed black it was on track.
So if you put it on a black sheet with a white line on it, it would end up anywhere on the sheet and would not follow the white line.
If you use two sensors and follow the edge then it probably doesn't make any difference whether it's on a black sheet with a white line or a white sheet with a black line.
i am using CCSC C programming..u mean u wanna use the UART function by RS232? i never try before.. but i think i can control the stepper motor by varying the PWM of the PIC..