Delete the center point in the bar with the color gradient (saves the effort of setting it to white).
Activate manual editing of the transfer function (the gear at the bottom of the colormap display, here shown for a different colormap).
``Enable opacity mapping for surfaces`` in the checkboxes below the bar.
Set the R/G/B values to 1 in the ``Color transfer function values`` section, and reduce the maximum opacity to 0.8 in the ``Opacity transfer function``. Play with the opacity value to find your favorite compromise between visibility of clouds and background.