nano highlighting fails in matching shell array brackets

The last two array expansions don't get proper highlighting:  This is the setting in sh.nanorc that defines it: # More complicated variable names; handles braces and replacements and arrays. color brightred "\$\{[#!]?([-@*#?$!]|[0-9]+|[[:alpha:]_][[:alnum:]_]*)(\[([[:space:]]*[[:alnum:]_]+[[:space:]]*|@)\])?(([#%/]|:?[-=?+])[^}]*\}|\[|\})" What do I have to fix in the regex to catch this miss?