docs: explain the 'set scrollercolor' option, for coloring the indicator

And mention that a background color does not work on libvte before 0.55.

To find out the version of libvte on your system:

  ls -R1 /usr/lib | grep libvte | grep 00 | grep -o "0\..."

doc/nano.texi

@@ -974,6 +974,12 @@ Regular expressions in @command{nano} are of the extended type (ERE).
 Save a changed buffer automatically on exit (@kbd{^X}); don't prompt.
 (The old form of this option, @code{set tempfile}, is deprecated.)
 
+@item set scrollercolor @var{fgcolor},@var{bgcolor}
+Use this color combination for the indicator alias "scrollbar".
+(On terminal emulators that link to a libvte older than version 0.55,
+using a background color here does not work correctly.)
+@xref{@code{set functioncolor}} for valid color names.
+
 @item set selectedcolor [bold,][italic,]@var{fgcolor},@var{bgcolor}
 Use this color combination for selected text.
 @xref{@code{set functioncolor}} for valid color names.

doc/nanorc.5

@@ -261,6 +261,12 @@ Regular expressions in \fBnano\fR are of the extended type (ERE).
 Save a changed buffer automatically on exit (\fB^X\fR); don't prompt.
 (The old form of this option, \fBset tempfile\fR, is deprecated.)
 .TP
+.B set scrollercolor \fIfgcolor\fB,\fIbgcolor\fR
+Specify the color combination to use for the indicator alias "scrollbar".
+(On terminal emulators that link to a libvte older than version 0.55,
+using a background color here does not work correctly.)
+See \fBset titlecolor\fR for more details.
+.TP
 .B set selectedcolor \fR[\fBbold,\fR][\fBitalic,\fR]\fIfgcolor\fB,\fIbgcolor\fR
 Specify the color combination to use for selected text.
 See \fBset titlecolor\fR for more details.

doc/sample.nanorc.in

@@ -203,15 +203,18 @@
 # set errorcolor bold,lightwhite,red
 # set selectedcolor lightwhite,magenta
 # set stripecolor ,yellow
+# set scrollercolor cyan
 # set numbercolor cyan
 # set keycolor cyan
 # set functioncolor green
+
 ## In root's .nanorc you might want to use:
 # set titlecolor bold,lightwhite,magenta
 # set statuscolor bold,lightwhite,magenta
 # set errorcolor bold,lightwhite,red
 # set selectedcolor lightwhite,cyan
 # set stripecolor ,yellow
+# set scrollercolor magenta
 # set numbercolor magenta
 # set keycolor lightmagenta
 # set functioncolor magenta

syntax/nanorc.nanorc

@@ -8,8 +8,8 @@ color brightred ".*"
 
 # Keywords
 color brightgreen "^[[:space:]]*(set|unset)[[:space:]]+(afterends|allow_insecure_backup|atblanks|autoindent|backup|backwards|boldtext|breaklonglines|casesensitive|constantshow|cutfromcursor|emptyline|finalnewline|historylog|indicator|jumpyscrolling|linenumbers|locking|morespace|mouse|multibuffer|noconvert|nohelp|nopauses|nonewlines|nowrap|positionlog|preserve|quickblank|quiet|rawsequences|rebinddelete|regexp|saveonexit|showcursor|smarthome|smooth|softwrap|suspendable|tabstospaces|trimblanks|unix|view|wordbounds|zap)\>"
-color yellow "^[[:space:]]*set[[:space:]]+((error|function|key|number|selected|status|stripe|title)color)[[:space:]]+(bold,)?(italic,)?(bright|light)?(white|black|red|blue|green|yellow|magenta|cyan|normal|pink|purple|mauve|lagoon|mint|lime|peach|orange|latte)?(,(light)?(white|black|red|blue|green|yellow|magenta|cyan|normal|pink|purple|mauve|lagoon|mint|lime|peach|orange|latte))?\>"
-color brightgreen "^[[:space:]]*set[[:space:]]+(backupdir|brackets|errorcolor|functioncolor|keycolor|matchbrackets|numbercolor|operatingdir|punct|quotestr|selectedcolor|speller|statuscolor|stripecolor|titlecolor|whitespace|wordchars)[[:space:]]+"
+color yellow "^[[:space:]]*set[[:space:]]+((error|function|key|number|scroller|selected|status|stripe|title)color)[[:space:]]+(bold,)?(italic,)?(bright|light)?(white|black|red|blue|green|yellow|magenta|cyan|normal|pink|purple|mauve|lagoon|mint|lime|peach|orange|latte)?(,(light)?(white|black|red|blue|green|yellow|magenta|cyan|normal|pink|purple|mauve|lagoon|mint|lime|peach|orange|latte))?\>"
+color brightgreen "^[[:space:]]*set[[:space:]]+(backupdir|brackets|errorcolor|functioncolor|keycolor|matchbrackets|numbercolor|operatingdir|punct|quotestr|scrollercolor|selectedcolor|speller|statuscolor|stripecolor|titlecolor|whitespace|wordchars)[[:space:]]+"
 color brightgreen "^[[:space:]]*set[[:space:]]+(fill[[:space:]]+-?[[:digit:]]+|(guidestripe|tabsize)[[:space:]]+[1-9][0-9]*)\>"
 color brightgreen "^[[:space:]]*bind[[:space:]]+((\^([A-Za-z]|[]/@\^_`]|Space)|([Ss][Hh]-)?[Mm]-[A-Za-z]|[Mm]-([][!"#$%&'()*+,./0-9:;<=>?@\^_`{|}~-]|Space))|F([1-9]|1[0-9]|2[0-4])|Ins|Del)[[:space:]]+([a-z]+|".*")[[:space:]]+(main|help|search|replace(with)?|yesno|gotoline|writeout|insert|browser|whereisfile|gotodir|execute|spell|linter|all)([[:space:]]+#|[[:space:]]*$)"
 color brightgreen "^[[:space:]]*unbind[[:space:]]+((\^([A-Za-z]|[]/@\^_`]|Space)|([Ss][Hh]-)?[Mm]-[A-Za-z]|[Mm]-([][!"#$%&'()*+,./0-9:;<=>?@\^_`{|}~-]|Space))|F([1-9]|1[0-9]|2[0-4])|Ins|Del)[[:space:]]+(all|main|search|replace(with)?|yesno|gotoline|writeout|insert|ext(ernal)?cmd|help|spell|linter|browser|whereisfile|gotodir)([[:space:]]+#|[[:space:]]*$)"