I “think” (this is Mr. FatFinger) there might be a typo in the web version of the Ch 19/Displacement. Attached is the image I just cut from my browser. Note that in the first code window you set the out.color to the height texture red channel. In the next code window, you override that color (I think) with BLACK and “highlight” patchID 0 with red. The resultant app image is an all BLACK “mountain” with a RED patch, however, the text in the website mentions and shows a grey shaded “mountain”. I was able to reproduce the web supplied image by removing the BLACK color “override” (I left the RED patch in). Please feel (very) free to delete this note when you point out what I’m seeing is not correct 
thanks for your feedback, @petenish ! I suspect @Caroline will see this here - she is always on top of her books.
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The second code window is code you should remove. It was only there to demonstrate that you can identify each patch.
Next, remove the following code from the end of the vertex function
You’re assigning the height map value to out.color , so you should remove any further assignment.
The book should probably boldface the remove because I miss it all the time too 
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