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.

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 → Noise → Difference Clouds….

This script has no option.