Difference Clouds command changes colors partially in cloud-like areas: The filter renders Solid Noise cloud in an automatically created new layer, and sets the layer mode to Difference, then merges this layer over the specified image.

Before merging the layer, this script opens the dialog of the Solid Noise plug-in which allows to control its effect.

If the image is in indexed colors, this menu entry is grayed out and unavailable.

This filter is found in the image window menu under Filters → Render → Clouds → Difference Clouds….

This script does not have its own dialog window but invokes the Solid Noise filter's dialog.