LaTeX writer/template: be sensitive to filecolor variable.

`linkcolor` only affects internal links, and `urlcolor` only
affects linked URLs.  For external links, the option to use is
`filecolor`.

Closes #4822.

MANUAL.txt

@@ -1526,12 +1526,14 @@ LaTeX variables are used when [creating a PDF].
 :    options to pass to the microtype package
 
 `colorlinks`
-:   add color to link text; automatically enabled if any of `linkcolor`, `citecolor`,
-    `urlcolor`, or `toccolor` are set
+:   add color to link text; automatically enabled if any of
+    `linkcolor`, `filecolor`, `citecolor`, `urlcolor`, or `toccolor` are set
 
-`linkcolor`, `citecolor`, `urlcolor`, `toccolor`
-:   color for internal links, citation links, external links, and links in table of contents:
-    uses options allowed by [`xcolor`], including the `dvipsnames`, `svgnames`, and `x11names` lists
+`linkcolor`, `filecolor`, `citecolor`, `urlcolor`, `toccolor`
+:   color for internal links, external links, citation links, linked
+    URLs, and links in table of contents, respectively: uses options
+    allowed by [`xcolor`], including the `dvipsnames`, `svgnames`, and
+    `x11names` lists
 
 `links-as-notes`
 :   causes links to be printed as footnotes

data/templates/default.latex

@@ -183,6 +183,7 @@ $endif$
 $if(colorlinks)$
             colorlinks=true,
             linkcolor=$if(linkcolor)$$linkcolor$$else$Maroon$endif$,
+            filecolor=$if(filecolor)$$filecolor$$else$Maroon$endif$,
             citecolor=$if(citecolor)$$citecolor$$else$Blue$endif$,
             urlcolor=$if(urlcolor)$$urlcolor$$else$Blue$endif$,
 $else$

src/Text/Pandoc/Writers/LaTeX.hs

@@ -248,7 +248,8 @@ pandocToLaTeX options (Pandoc meta blocks) = do
                                      defField "biblatex" True
                          _        -> id) $
                   defField "colorlinks" (any hasStringValue
-                           ["citecolor", "urlcolor", "linkcolor", "toccolor"]) $
+                           ["citecolor", "urlcolor", "linkcolor", "toccolor",
+                            "filecolor"]) $
                   (if null dirs
                      then id
                      else defField "dir" ("ltr" :: String)) $