: In the Channels palette, click on the Cyan channel. Go to the Filters menu and you’ll notice that all those grayed-out filters are now suddenly available. All you have to do now is apply the filter you want to each channel individually (once each on Cyan, Magenta, Yellow, and finally the Black channel), and the filter will appear as though you applied it to the entire image (in reality, you did—you just did it the more laborious way). One way to speed up this process is to create an action that will do it all for you with one click of the mouse.