The Color Key effect keys out all image pixels that are similar to a specified key color. This effect modifies only the alpha channel of a clip.

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Nonstandard blue screen (left) and background (center) are combined with Color Key (right).

When you key out a color value in a clip, that color or range of colors becomes transparent for the entire clip. Control the range of transparent colors by adjusting the tolerance level. You can also feather the edges of the transparent area to create a smooth transition between the transparent and opaque areas.