xor raphael.js stroke color

[helyi]

When I am using Rafael.js to draw rectangles, I set the color of the outline using\[code\]Canvas.rect.attr({stroke: 'red'});\[/code\]where Canvas is made using \[code\]Canvas = Raphael(xOffset,yOffset,width,height);\[/code\]However, when I am using this to draw rectangles on images, the background may be the same color as what I set for the stroke color making the rectangle difficult to see.I was wondering if there is a way to automatically/dynamically give the rectangles maximum contrast with the background, such as making the stroke color XOR with the background. That is, is there a way to automatically make the stroke color light when the background is dark or vice versa or to make the stroke color the color complement of the background.