$canvas->createRectangle(
int $x, int $y, int $x, int $y,
                         -outline=>undef,
                         -fill=>'white' );

#to (or any variation), you need an outline color and size

$canvas->createRectangle(
int $x, int $y, int $x+1, int $y+1,
                         -outline=>'lightgreen',
                         -fill=>'white' );