Are you actually referring to formal
- formal (=full dress, ie morning dress/Cutaway (day) and white tie/tailcoat/Frack (eve)) and
- semi-formal (=half dress, ie stroller/Stresemann (day) and black tie/tux/Smoking (eve)) attire,
or informal formal (ie suits)?
If an office policy is semi formal, do people turn up in a black tie?
Why are black tie parties "black tie" parties and not "semi formal" parties?
IMO you've listed "opera" followed by "black tie."
"Formal" would be "a tie and jacket," "semi formal" would be a jacket without a tie, or (shudder) a tie without a jacket, and then business casual is where the polos come in.
All pants are black: All shirts are black or darkish grey. I'm also female, and find fashion rules confusing.