Edit: /usr/share/nano/nanohelp.nanorc (418B)
## This is meant for highlighting key combos in a nano help text.
# It should not apply to any normal file, so no fileregex.
syntax nanohelp
# Key combos:
color cyan "\^[]/4-8@A-Z\^_`◀▶▲▼]" "[◀▶▲▼]" "\<(M|S[Hh]-[Mm])-." "\
"
# Quoted indicators:
color brightred "'(\^|M-)'"