look at the bottom of the two lines
To make the line appear smooth, intermediate colors between the color of the background and the line have been added at its edge. In this case, black has been anti-aliased to white. What if I wanted to crop an anti-aliased shape (like the line on the bottom) but correct the anti-aliasing color to that of its new background? So if the background were blue, how could I change the black-white anti-aliasing to black-blue?
Essentially, I have a red shape that has edges that fade to a white background, and I want to move it onto a black background and correct its edges to fade to black. What tools can I use to do this?