That will find and highlight only the first match, then move on to the next line of code. It appears the OP wants to highlight *all* of the search terms in the document while preserving case.

The secret, as my fellow monks have pointed out, is using parenthesis to collect the match on the left hand side of the substitution and the special variable $1 to insert that match on the right hand side. Read more about it in perlre.

(Yes, code needs explanation of the mechanics, sometimes.)