Simplicity uses green screen for several reasons. Sometimes because they want to publish a pattern in the most current prints available which might not be ready when the samples are being made. Sometimes because they want to be able to take a bunch of extra photos during the photo shoot and use some of those photos later in what they call an editorial shot in the catalog sometime in the future. They can then use a print that might not have been available at the time of the photo shoot.
When this technology was first available, Simplicity was using it much more than they do now. It doesn't save as much time as they thought it would in most cases. It's very tedious manipulating a print into all the nooks and crannies of a garment or home dec item so that it looks natural. But, it is a great technology in certain places.
Here are a couple other designs of mine that have been color mapped.