>>>I have an app where I am cropping images. Everything works great thanks to GdiPlusX. I create a shape object with MouseDown / MouseMove to mark the crop area. My question is how to get the contrasting color so the shape border will show against all the different colors in the image. I know I can get the color at the mouse down point but how do I get a light color if the image is dark, etc. I assume this is an easy one if you know what you are doing.
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>>What if you use XOR operation to draw the selection box border?
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>I looked at that but how would I use it. I have one value; the current color. What would be the 2nd value?

Try

lnNewColor = BITXOR(lnCurrentColor, 0xFFFFFFFF)