With a modification in Texinfo to add the location of @example commands 
to the "Tags Table" of Info files, and some lisp to search that and 
propertize text, I'm getting the results in the attached images (with 
and without the code colors).

To take advantage of this, Texinfo files need to indicate the language 
used on the example so we know how to fontify.  Also, uses of 
@smallexample should change to @example.  The Lisp Intro uses 
@smallexample a lot. If no language is specified, we still get the gray 
box around the code.

Now I need to take this change (which will take some work) to the 
Texinfo developers, if it looks worth the effort.