What should I wear to the gala?

I will be attending my first gala this month. It is a charity gala, and it will be a big event.

I’ve been googling up about what to wear to galas, and it seems that a lot of sites will say to wear “the best dress you have”.

So, I just wanted some more opinions from Fluther. I’m feeling keen on wearing a dark blue ball gown that I own, and wore for my grade 12 graduation banquet, but if not, I also own many more dresses. Including, a black evening gown.

Have you attended any galas before? What is the norm for females? Should I wear my Ball gown, or another dress?

Thanks in advance! :)