Images with curved, smooth edges, like the one in this example, maintain the illusion of crisp edges as a result of anti-aliasing—partially transparent pixels are added onto the edges of the image to smooth them, as shown here. However, when you save an image as a GIF, these partially transparent pixels are saved as non-transparent pixels where white is the default "background" color.

Close-up of anti-aliased shape

If you're not placing this image on a white background, it might be wise to define a custom matte color by clicking on the Matte arrow, as shown here. Otherwise, you'll end up with a white "color halo" around the image.

Choosing alternate matte color

Let's say that we're going to place this graphic against a bright red background. Click on the Matte arrow, choose Other., and select a bright red.

Setting a bright red matte color

Now you'll be able to see a red color halo around the graphic. If you zoom in, you'll see that those anti-aliased pixels behave as though they're sitting on a red background.

Click the Save button to save your image.

Close-up of color halo

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