[water]

i don't think formal necessarily means a black tie. i think any colour of ties is good.

with semi-formal, u can just wear a khaki pant plus a good shirt with collars. formal u have to wear a suit.

for girls, i'm not very sure.

i think black tie is just an expression..
it's not literally "black" tie..
i think it's cuz in the old days the ties are always black, there's no colours for ties~
so that's why they call it a black tie event, but doesnt mean u have to wear a tie that's black~