You have to turn off each color individually in separation preview .
With Photoshop you only need to click on a color. Hold down the mouse button and then pull it up or down to switch more colors on or off. So if you want to switch 10 colors off and on again, for example, you have to click the mouse a total of 20 times.
With Photoshop you only need two clicks for this process.
Why isn't this done at Illustrator?