Make a color transparent with Color Key

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 layer.

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.

Select a clip in a Timeline panel.
Apply the Color Key effect to the clip.
In the Effect Controls panel, click the triangle to expand the Color Key effect.
Do one of the following to specify the key color:
- Click the Key Color swatch to open the Adobe Color Picker, select a color, and then click OK.
- Click the Eyedropper icon, and then click a color on the computer screen.
Drag the Color Tolerance slider to specify the range of color to key out. Lower values key out a smaller range of colors near the key color. Higher values key out a wider range of color.
Drag the Edge Thin slider to adjust the width of the keyed area’s border. Positive values enlarge the mask, increasing the transparent area. Negative values shrink the mask, decreasing the transparent area.
Drag the Edge Feather slider to specify the softness of the edge. Higher values create a softer edge but take longer to render.