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Does anyone know if there's an easy way to make a negative? In other words, I have a black and white image, and I'd like to make all the blacks white and vice versa. Thanks!
Select all the white objects and click a colour (let's say red) on the swatches palette, just not black (otherwise the entire pic will turn black and you can't make a good selection anymore). Then select all black objects and make them white by clicking white on the swatches palette. Next, select all red objects (originally white) and click on black in the swatches palette... done
Very cool. I've been using Illustrator for about 6 years now and I had no idea that function existed. Unfortunately it doesn't work with Global colors, spot, or gradients, but still useful. It's a neat way of coming up with color combos.
As for the original question I was going to suggest building your design with global colors. Then when you want to reverse simply double click the swatches and change the colors to their opposite. All instances of that color in the design will change. I almost always build my art with global colors.
Easy way to make a negative? 
