Contrast clouds
Pressing the Option (PC: Alt) key when invoking the Clouds filter (Filter>Render>Clouds) will increase the contrast between the Foreground and Background colors, giving you clouds with a higher contrast.
Immediately following the cloud rendering, if you press Command-Option-F (PC: Ctrl-Alt-F), you'll get clouds with even more contrast. Press this key combination as many times as you like until your clouds are visually appealing. from Bert Monroy
thanks for this tip…really helpful if I want to make some cool effects