Spray on cleaners used in households can cause serious damage to curtain fabrics.
Many fabrics are not colour fast and many of these cleaners will either change or remove the colour from the fabric.
Sometimes this may not be noticeable until the curtain gets wet, either when being cleaned or through water ingress at the window.
There is no way to remedy this and the curtain will remain damaged.
The pictures below show what happens.
Splotches show where colour has been stripped from the curtain material.