syntax: nanorc: properly color valid arguments of 'selectedcolor'

This fixes https://savannah.gnu.org/bugs/?52114.

syntax/nanorc.nanorc

@@ -8,7 +8,7 @@ icolor brightred "^[[:space:]]*((un)?(bind|set)|include|syntax|header|magic|comm
 
 # Keywords
 icolor brightgreen "^[[:space:]]*(set|unset)[[:space:]]+(allow_insecure_backup|atblanks|autoindent|backup|backwards|boldtext|casesensitive|constantshow|cutfromcursor|fill[[:space:]]+-?[[:digit:]]+|historylog|justifytrim|linenumbers|locking|morespace|mouse|multibuffer|noconvert|nohelp|nopauses|nonewlines|nowrap|positionlog|preserve|quickblank|quiet|rebinddelete|rebindkeypad|regexp|showcursor|smarthome|smooth|softwrap|suspend|tabsize[[:space:]]+[1-9][0-9]*|tabstospaces|tempfile|unix|view|wordbounds)\>"
-icolor yellow "^[[:space:]]*set[[:space:]]+((function|key|number|status|title)color)[[:space:]]+(bright)?(white|black|red|blue|green|yellow|magenta|cyan)?(,(white|black|red|blue|green|yellow|magenta|cyan))?\>"
+icolor yellow "^[[:space:]]*set[[:space:]]+((function|key|number|selected|status|title)color)[[:space:]]+(bright)?(white|black|red|blue|green|yellow|magenta|cyan)?(,(white|black|red|blue|green|yellow|magenta|cyan))?\>"
 icolor brightgreen "^[[:space:]]*set[[:space:]]+(backupdir|brackets|functioncolor|keycolor|matchbrackets|numbercolor|operatingdir|punct|quotestr|selectedcolor|speller|statuscolor|titlecolor|whitespace|wordchars)[[:space:]]+"
 icolor brightgreen "^[[:space:]]*bind[[:space:]]+((\^([[:alpha:]]|[]0-9\^_]|Space)|M-([[:alpha:]]|[]!"#$%&'()*+,./0-9:;<=>?@\^_`{|}~-]|Space))|F([1-9]|1[0-6])|Ins|Del)[[:space:]]+[[:alpha:]]+[[:space:]]+(all|main|search|replace(with)?|gotoline|writeout|insert|ext(ernal)?cmd|help|spell|linter|browser|whereisfile|gotodir)([[:space:]]+#|[[:space:]]*$)"
 icolor brightgreen "^[[:space:]]*unbind[[:space:]]+((\^([[:alpha:]]|[]0-9\^_]|Space)|M-([[:alpha:]]|[]!"#$%&'()*+,./0-9:;<=>?@\^_`{|}~-]|Space))|F([1-9]|1[0-6])|Ins|Del)[[:space:]]+(all|main|search|replace(with)?|gotoline|writeout|insert|ext(ernal)?cmd|help|spell|linter|browser|whereisfile|gotodir)([[:space:]]+#|[[:space:]]*$)"